Makes perfect sense for Khamzat. He took virtually no damage in the fight with DDP, and would do well to stay active and re-ignite the fanbase after his somewhat polarizing method of victory left a portion of it 'unsatisfied' (plus, he claims to want money, so why sit around and wait for the Imavov-Caio winner?). Plus, why let RDR have more time to specifically prepare for him? Knock him off now, with him recently coming off a tough fight.
Yep, RDR probably could use more time off to recover and to prepare for a very different fight than it would have been had DDP remained champ...but that is not Khamzat or the UFC's problem though.
UFC will probably go to RDR and offer Abu Dhabi as his opportunity to bypass competing with the Imavov-Caio winner for a shot...if he doesn't take it, they will say he will have to fight again to *maybe* get a title shot afterwards. If he turns it down, Fluffy is there...and while Costa clearly doesn't deserve a shot right now, the UFC loves having options for leverage.
If Khamzat wants his Abu Dhabi fight, he will get it...and I would be very surprised if RDR turns it down if it is offered to him.