I am actually in the unique position of being an MMA fan, a wrestling fan, and a boxing fan all at once. How, some of you diehards may ask? Well, it's because I'm able to put each into it's own context. I know what to expect from each one, and it's not going to remain the same for any of the others. I simply don't expect takedowns in a boxing match, one punch knockouts in wrestling, or Stone Cold Stunners in an MMA fight, and that's how I enjoy each one.
However, I do believe there are some people in wrestling who could have easily crossed over into MMA if they had done it at a good age. Right of the top of my head, I would say Kurt Angle, Bret Hart, Chris Benoit, Taz, William Regal, and even the Undertaker could have crossed over into MMA at a younger age, closer to their prime and have had some success. Angle is a world-class freestyle wrestler with phenomenal athleticism, work ethic, intelligence, and power, and for damn sure, a ton of heart. Hart, Benoit, Regal, and Taz were all proficient in the same catch wrestling that another former pro wrestler named Kazushi Sakuraba was proficient in and used to great success. Taz himself, I believe, is a legit judo black belt. As for Taker, he's a huge MMA fan who is remarkably athletic for a man his size and could easily immerse himself into MMA and become good at it. That, and he dabbles a bit as it is in his advanced age in both boxing and BJJ that he is more than comfortable showing it in any of his wrestling matches. At a younger age, Taker could have done MMA and done very well.
And then there's a lot of MMA guys who could do very well in wrestling. Shamrock was already there and did very well for the time he was there. Tito Ortiz, Andrei Arlovski, Aleksander Emelianenko, Rampage, and Mayhem Miller all have either the right look or the right personality or the right mentality, or a combination of all three to succeed in pro wrestling.