I'll be hyped about GTA 6 either way, and returning to Vice City would be cool... but a whole new area would be more exciting imo.
San Andreas is one of my favourite games of all time, but I got no real enjoyment out of the fact that GTA 5 was also set in SA/Los Santos.
I was hyped about the return to San Andreas prior to the game's release, but playing the game it just felt like a totally different vibe to me (not in a bad way necessarily) than San Andreas.
Being set 21 years apart from each other might account for that though. Still loved the game regardless, but yeah.
I feel like it'd probably be a similar story with a return to VC.
I think something totally original would be better personally.
Would absolutely love a new GTA set in a different country, England perhaps.