Cormier looked very lackluster against Mir and against Nelson he looked like he was far less than stellar. Nelson has a great chin and KO power with good BJJ but that's it. He isn't 6'5 with an 81.2" reach and a granite skull who can move like a welterweight. Cormier would have a bitch of a time trying to setup a takedown on a guy like Gustafsson, trust me. Jon Jones learned this himself, the hard way. Even the chain-wrestling Cormier showed against Nelson to eventually get him down would be nil because Gustafsson would never give him the chance. He'd shrug off the first attempt and move out of the way, cut angles, and sting him like a bee. Jones' takedowns are leagues better than Cormier's (Olympian or not). Jones has very solid freestyle, Greco and Judo takedowns. Cormier doesn't have all of this, which he'd need.
I'd welcome this match-up though. At least it'd get Cormier's hype out of the way. Cormier hasn't been nearly as impressive as Jones or Gustafsson in the UFC whatsoever. That won't change, he gasses after a couple rounds completely.