Personally, I don't really see an ideal option for a first defense. Vitor hasn't earned it, but it's always fun to see a good "what goes around comes around" scenario. That dude has earned all the beatings he's going to take post-juice.
Straight up, Yoel Romero has shown that he and his camp are flagrant cheaters across multiple fights now. Despite that and the questionable decision in his favor last night, the matchup still makes the most sense but still... fuck that dude.
Weidman doesn't deserve a rematch after that performance and it makes the most sense to match him up with Jacare in a title eliminator. Still, he did defend the belt multiple times and there really isn't anyone else outside of him, Romero, and Belfort who can be considered currently in the title hunt. Next closest guy is probably Machida and he's dropped three of his last five fights (including his last two) if I'm not mistaken.
I mean, who else is there right now? Robert Whittaker? Fucking Michael Bisping? Who else with any relevance in the division is coming off a win?