I agree on paper he's the hardest challenge so far. I disagree that he'll get out of GSP top control though. What do you base this on? His college experience? GSP is not getting swept and he's not getting overpowered, if GSP is on top he'll stay on top.
There's a big difference between collegiate level wrestling and MMA wrestling. I've no doubt in a straight wrestling match that Hendricks could prob win it. The reason why no one can avoid GSP's takedown is because in MMA you can hit the guy. This guessing game of strike up down / take down along with GSP's impeccable technique/timing is the reason why nobody can stop his takedown.
On the ground, MMA wrestling also differs because now you got to deal with Jitz tech which you didn't have to worry about before. Having collegiate experience for wrestling gives the same benefit as a golden glove boxer would have on his striking technique. It's great to have but it just starts them at a non scrub level with the MMA version.
Lastly, I'm surprised no one tried to Sonnen GSP just yet. Seriously, everyone knows his throws pillow punches so why not bull rush him 5 sec into the fight? You're gonna get hit by a few shots for sure but once you body lock him, it IS possible to take him down. GSP is prob no slouch on his back but I'm positive that's the last place he'd want to be in. If i was Hendricks, I'd toss striking out the window and just bull rush him from the start and try to Sonnen GSP.