Personally I would love for PoE3 to go back to the PoE1 style of gameplay and push it even further into the per-rest realm than that game was but yeah, that's never gonna happen.
Anyways, I'm not normally a huge fan of sequels continuing the story of a character. But I do think it'd be nice to get a final chapter in the Watcher's story, and see what happens after the events of Deadfire. I think there are a lot of cool things that could happen and it'd be awesome to explore the repercussion of the events of Deadfire among both kith and gods.
Maybe have the tables changed on the gods somehow so that they are now put more into a place of submission rather than ordering people around like in PoE1 and 2, and you'd have to decide if you want to help them or not. I dunno, it could go to a lot of cool places.
I would definitely welcome other stories in the Pillars universe as well, but yeah... I think it'd be great to have a good conclusion to the Watcher's story, as well as what will happen to Eora after Deadfire.