I personally think it is going to be somebody with a really technical defensive stand-up game, with offensively the ability to either get in really quick or to strike from a distance.
Foot work is the key. So i would have to say either shogun or rampage. Page has always excelled against counterpunchers by parrying and counter punching them with explosive bursts forward getting him into his striking range. Machida has the footwork and relfexes to back out, but for how long? if he can do it for 5 rounds then its his but at some point i think page would catch him.
And shogun i feel can strike with him from outside machidas punching range with his kicks, allowing him to not have to risk getting hit just to set up an offense. Not to mention his kicks are a better than machida's. This will force machida to try something new, something more aggressive.
Ive been thinking about wanderlei v. machida since the jardine fight and have changed my tune from wanderlei to machida having the advantage. Wanderlei if he connects right can put anybody out, but when he throws he sets his feet and hes stationary as hes swinging. This plays well against fighters that come forward like rampage or fighters with just a general lack of footwork like jardine, but machida always sticks and moves, hes moving away at all times and his footwork and mobility far exceed wanderlei's. If wanderlei decided to chase machida i think machida would become really active, as wanderlei leaves himself open when he swings wide Machida will have plenty of opportunites to sneak in punches. He did the same against Franklin. Also when Wandy is chasing how is his power going to be affected? his feet arent going to be placed firmly, his motion for throwing those bombs will be disturbed. That one punch mega power will fade without his feet under him properly.
...just my thoughts