Some people definitely have an opinion when it comes to what sports should be included in the Olympics. Synchronized swimming and rhythmic gymnastics are popular targets, but non-TV-friendly sports like flat-water canoeing and the modern pentathlon also take some heat.

But what about the sports that didn't make it into this year's Summer Games? The inclusion of golf and rugby sevens in the Rio Olympics shows that the International Olympic Committee (IOC) is not opposed to changing the program. These new gold medal sports raise questions about what could be around the corner. What other competitions would be a good fit for the Games? Which sports have the international popularity, accessibility and TV-friendliness to generate more interest in the Olympics?

You won't see these sports at the Rio Games, but they could be a good fit for future Olympics.

1. Parkour

Joel Eggimann of Switzerland performs during the finals at the 'Red Bull Art of Motion' freerunning competition Parkour is a young sport, but there are organized competitions, like Red Bull's 'Art of Motion' event. (Photo: Predrag Vuckovic/Getty Images)

Developed in France and popularized during the 1990s and early 2000s, parkour is often praised for its universal accessibility. The sport, which is also known as freerunning, involves moving through (usually) urban environments as quickly and creatively as possible. No special equipment is required, making the sport accessible to people all over the world. A recent news story, for example, noted the growing popularity of parkour in Afghanistan.

As a competitive sport, parkour is just a baby. Some professional events are hosted by the likes Red Bull, but the judging criteria is still rather subjective. A lot has to develop before parkour practitioners can compete for gold medals, but if the IOC is serious about being more inclusive, accessible low-entry-cost sports like parkour should be on the Olympic program sooner rather than later.

2. Cricket

MS Dohni of India hits out as Jos Buttler of England looks on during the NatWest International T20 2014 match between England and India Only one cricket format, T20, is short enough to be played at the Olympics. Here, MS Dohni of India hits out as Jos Buttler of England looks on during a NatWest International T20 2014 match.(Photo: Clive Mason/Getty Images)

Cricket is known for its multi-day games. It is true that traditional "test" matches can last for five days, so it would be impossible to host a multi-team test cricket tournament during the two-week-long Olympics. However, shorter formats of the game have become more popular in modern times. These days, three-hour T20 matches draw the most interest from fans. This shorter form of cricket could realistically be included in the Olympics.

Many people argue that cricket should be included in the games because of the number of people who follow it. Well over a billion fans watched the recent World Cup held in Australia and New Zealand. Cricket is the number one sport on the Indian subcontinent and in the Caribbean, and it is very popular in the U.K., Australia, South Africa and other Commonwealth countries.

3. Surfing

Surfing has long been popular in oceanside regions. It is one of the most popular sports, both competitively and recreationally, in Australia, Hawaii, California, Indonesia and Brazil. There is already serious momentum for getting surfing into the Olympics now that sports like BMX racing and snowboarding have been included in the Summer and Winter Games, respectively.

Not only is surfing an international sport, but, unlike parkour, it has a well-established system of judging and scoring and a set of global and regional tours that draw a huge number of spectators to events held on six different continents. The International Surfing Association is banking on this worldwide appeal to help it as it faces the final round of voting for inclusion in the 2020 Olympics in Tokyo.

4. Bowling

Tannya Roumimper throws the ball during the Asian Games 2006 bowling women's singles competition Bowling is already included in regional sporting events like the Asian Games. (Photo: Toshifumi Kitamura/Getty Images)

Bowling certainly has the numbers to support its case for Olympic inclusion: 100 million people have played the game, and 10 million of those compete in some sort of league on an amateur or professional level. Furthermore, there are well-established international competitions and professional tours all over the world.

Bowling's governing body, World Bowling, has been testing out new, easier-to-understand scoring in order to, hopefully, make the sport more attractive to the IOC. Like surfing, bowling applied to be part of the 2020 Olympics in Tokyo. Unfortunately, it failed to make the final cut, so it will be at least eight years before bowlers can realize their dream of rolling for Olympic gold.

5. Croquet

An older woman plays croquet Croquet is one of the more accessible sports that could be (re)introduced into the Olympics. (Photo: Dan Kitwood/Getty Images)

Most people think of croquet as a game that is played during backyard barbecues, but it was once popular enough to be included in the games. It was part of the Olympics in Paris in 1900. The female players who participated in the 1900 tournament were among the first women to compete in the Olympics in the modern era.

There is a governing body for croquet called the World Croquet Federation (WCF). World championships take place every other year, on average. Most of the top ranked players are from Commonwealth countries, but the limited equipment requirements and the fact that players can hone their skills in their backyard (though there are more than 200 croquet clubs in the United States) makes this one of the more accessible sports on the list.

6. Skateboarding

 A competitor hand-plants off the top of the ramp during Converse Coastal Carnage skateboard event Skateboarding could be a part of the IOC’s effort to appeal to younger audiences. (Photo: Victor Decolongon/Getty Images)

Thanks to savvy marketing and youthful energy, skateboarding has caught on around the world. Professional circuits have allowed skaters to support themselves through prize money and sponsorships. More importantly when it comes to the Olympics, these competitions have helped develop a fair and uniform system of judging.

The IOC obviously wants to appeal to younger viewers. Sports like BMX and snowboarding are already part of the games. Skateboarding has passed the first round of the approval process for the 2020 Tokyo Olympics, so though it won't be seen in Rio this year, it could end up on the program four years from now.

7. Mixed martial arts

Rustam Khabilov of Russia (Black Shoirts) throws Norman Parke of Nortern Ireland during a UFC bout Mixed martial arts has moved into the sports mainstream over the past decade, but its violence and reputation with performance-enhancing drugs may make it a hard sell for the Olympics. (Photo: Christopher Lee/Getty Images)

Though the paydays for top ranked boxers are still much higher than they are for fighters in major mixed martial arts promotions like the UFC, MMA is now squarely in the mainstream. Major professional events are held all over the world, and fans can watch coverage of the sport on TV almost daily.

Many athletes who grew up competing in Greco-Roman wrestling or judo, both Olympic sports, have made the transition to professional MMA fighting. Unfortunately, for mixed martial artists with Olympic aspirations, some issues still stand in the way. The sport has experienced a major problem with performance enhancing drugs, with top contenders and title holders failing PED tests on more than one occasion. MMA's violent image could also be an issue for the IOC. Nonetheless, there is no denying the worldwide popularity of the sport, which might eventually compel the IOC to take a closer look.

8. Chess

Vishy Anand makes a move against British chess champion Michael Adams Even with barn-burner games like this one between super-grandmaster Vishy Anand and British chess champion Michael Adams, chess isn't exactly an exciting sport. (Photo: Carl Court/Getty Images)

Is it a "sport" or a "game"? Though it has not yet voted to include chess in the Olympics, the IOC officially recognizes the board game as a sport. Chess is undeniably popular on an international level. There are professional tournaments and a huge amateur player pool.

On the downside, chess is unlike any other Olympic competition. It lacks the TV-friendliness and youthful appeal that the IOC seems to favor these days. However, perhaps the main reason that chess has not been taken more seriously is that the International Chess Federation, the sport's governing body, has been involved in a number of scandals and has been the target of corruption allegations recently.

9. Sport climbing

Kim Jain competes in the Women's qualifying round of the indoor World Climbing Championships The International Federation of Sport Climbing (IFSC) hosts climbing competitions throughout the year. Pictured is South Korea's Kim Jain competing in the women's qualifying round of the indoor World Climbing Championships in 2012. (Photo: Miguel Medina/AFP/Getty Images)

Some people were surprised that sport climbing was included on the final list of sports being considered for the 2020 Summer Games. Though reports suggest it is a favorite to be voted in at pre-Rio IOC meetings, the sport's governing body, the International Federation of Sports Climbing, is campaigning like it is still a long shot to make the '20 Games.

Sport Climbing World Cup events are held throughout the year and climbing competitions are already a part of international meets like the University Games and World Games. IFSC has made major inroads throughout the world by hosting promotional events to bring more mainstream attention to the sport. This effort could be a major reason why the IOC is seriously considering climbing for the Tokyo Games.

10. Billiards

Austria's Jasmin Ouschan competes in the World 8-Ball pool championship 2008 Pool has an established professional circuit for both men and women. Pictured, Austria's Jasmin Ouschan competes in the World 8-Ball pool championship 2008. (Photo: Karim Sahib/AFP/Getty Images)

Pool, more formally known as pocket billiards, is very popular in certain parts of the world. Like bowling, there are plenty of amateur leagues and a high number of recreational players. The World Pool-Billiards Association (WPA) hosts annual world championships. The most popular form of competitive pool is nine-ball (different from standard pool-room eight-ball because balls must be pocketed in ascending order from 1 to 9).

Billiards is very popular in places like the Philippines and Italy. So-called cue sports are included in regional competitions like the Asian Games and Mediterranean Games. There has been an effort to include billiards in the Olympics since the 1950s. Some members of the IOC have voiced support for pool over the past decade, but this has yet to lead to anything.