Hendricks just needs to manage his weight better I think.
I'm not so sure he's got the frame to be able to compete at middleweight either. He's 5"9 with a 69 inch reach. Look at the top guys in the middleweight division: Weidman (6"2, 78in), Rockhold (6"3, 77in), Souza (6"1, 72in), Romero (5"10, 75in), Machida (6"1, 74in). All of them would dwarf Hendricks physically.
Which isn't to say it'd be impossible for him to win fights in that division (he gives up height and/or reach to a fair few welterweights too) but he'd be starting at a significant disadvantage against pretty much all of them.