In all honesty, I think that the person to beat Khabib will be Khabib. If he starts slacking, or looking towards retirement or whatever, he'll perhaps be there for the taking. As things stand, if he's 100% on his game, I don't think there's anyone at 155lbs who can beat him short of a fluke where he gets caught or something. The guy wins every fight in that division 9 times out of 10, if not 10 times out of 10. He's the greatest MMA fighter I've ever seen, that's for sure.