A Costa rematch is a very tough sell IMO. And I'm not even talking immediate. That was as one-sided a fight as you'll ever see. It wasn't a situation where a guy just got caught.
Not to go too psychologist but that fight gave a lot of insight into Costa's mind. Some guys are just born fighters, literally no fear. Hendo, Shogun, prime Wand, Fedor, probably put Chuck in there, etc. Then you have another group of guys who look like absolute killers until the going gets tough (Rumble for instance). Costa is in the second category. When he couldn't figure out the distance and those shots were landing and hurting his instinct was not to press forward, it was to retreat. Nothing will ever change that. Doesn't mean he could never beat Adesanya, but it makes it much tougher to sell a rematch. Romero for instance, he had absolutely zero fear in that fight. That rematch is an easy sell IMO.
I realize, much easier said than done, but I'll never understand why guys don't close distance with their hands glued to their head, elbows tucked, lots of feints and head movement, but essentially never exposed. Sure you'll probably eat a shot or two, but it will be easily blocked/defended. Now you're at a distance where Adesanya can't pick you apart. Now I realize beating Adesanya in the clinch, taking him down, pinning him to the fence, etc., are all easier said than done, but it's just not THAT hard to move forward while blocking to at least get to a range where you can attempt those things.