I believe Cormier will win, but I won't ignore the hight and reach differences either since they are so gapped here.
Cormier has 2 issues that I would like to see him fix or maybe take a lesson from his student Cain Velasquez: He seems rather vulnerable to kicks and knees. Have you seen his fight with Barnett and Mir? Barnett was at a point where he laid some offensive kicking and knees and boy did Cormier feel it and back up against the fence, he even squinted his eyes because the knee to his face hurt so bad, then Barnett stopped... If only he would have continued the knees and kicks he would come close to breaking down Cormier, but it's the fear of getting taken down is what prevented more of that I believe.
Next was with Mir, when Mir started to kick Cormier's body a few times in a row the Cormier went flying back into the cage and ate another kick and Cormier had no answer for it, he looked troubled by those kicks and was ready to eat more, then Mir stopped.... You get the point, go look at those fights again.
Jones would need to utilize fast kicks and avoid a take down by Cormier but I doubt that will be possible lol
The 2nd issue with Cormier is he doesn't put enough pace in some fights. He was just going back and forth with Mir, although successful, it was boring and he could have ended it quicker. Same with Barnett, although he owned Barnett, I'm not sure why he was holding back so much when he has the ability to run over these guys.
I say this because Jon Jones doesn't seem to handle pressure well so hopefully Cormier doesn't do the 'back and forth' thing but pursues like Cain. However Jon Jones does kick and knee pretty good which might help him a bit against Cormier.
The only reason I pick Cormier to win is primarily because of his Olympic wrestling and strength. It's just sad that those are the only things he has to keep him alive but it may wok for years to come.