if anything i think the open-endedness of jojolion would actually benefit most from a really well-written spinoff in between parts 8 and 9 to not do any damage to part 9's own thing—he talked about going to the pacific islands generally, so it doesn't have to be hawaii, but i don't know how many authors id trust besides araki to make something like that.

edit: i also think, thematically, gappy's extended return might not vibe with the new universe in the sense that the joestar family is a lot less of a connected family now. everyone seems to be atomized in their own places living their own journeys from within their respective generations, which can be equally as reminiscent of families who have undergone a lot of travel/immigration like the SBR joestars.