It is a pretty safe bet that more main roster talent will join NXT. I wasn't at all surprised to see Balor rejoin. He and KO were the key talent when NXT was at its hottest. I wouldn't be surprised to see KO back and trying to get that dynamic back again. Not easy though.
Wholesale return of NXT talent would not look good. It would look like a bunch of failures coming back to repeat a year
I think if they send back to. NXT but they still have the main roster contract (read: salary) then performer like Asuka will be happy to take it, anyone try to be realistic with the situation, NXT have less live event schedule more than main roster.