Hopkins is just too old. If he's allowed to fake a low blow every couple of rounds to make sure he gets through the 12 rounds then he'd probably win but if it's a fight where they just stick to the rules and don't **** around then he'd probably get stopped, possibly whilst ahead on the cards, through exhaustion as much as anything.
It depends in what country Hopkins UD in USA Kessler wide UD in Copenhagen something like 117-111 In reality I think Hopkins knows how to deal with fighters who come forward in straight lines, and Hopkins lateral movement would trouble Kessler even at this stage.