Personally I would rather not revisit older settings, unless we're doing a Jugdral -> Archanea -> Ylisse situation: we can wink wink nudge nudge at the connection between games, while having a long enough time gap that it still feels like a new place. Alternatively I like the Thracia approach: it's a fresh perspective even if the setting is technically the same.

Going through all the continents in order:

• Archanea: game + sequel, both got remakes and it got a (big time gap) prequel and sequel in GoTHW and Awakening, I think that's enough.

• Valentia: an extension of the Archanea world since it's the next door continent, partially revisited in Awakening as Valm, I don't see it being reused successfully in a new game.

• Jugdral: the two parts make it feel like it's a game with its own sequel built in, it got Thracia 776 as a side story in the same universe, and has the connection to Archanea and Ylisse. I love Jugdral, but that's enough.

• Elibe: game + prequel. Could use remakes (FE6 especially), but not before Jugdral, and I think 2 games is sufficient for each continent.

• Magvel: Magvel is pretty much the only fully standalone continent...and yet I don't want it to be revisited. I think it's fine as a self contained story, sometimes less is more.

• Tellius: game + sequel, meant to have a sequel from the get-go, and it shows. If they're going to revisit a setting, do it this way. I wouldn't want them to dig Tellius back out again.

• Ylisse: as said above. It's self contained but also not, and I think it's plenty. All they could do is prequels/alternate universes with Chrom's dad or the doomed timeline, but neither is a particularly good option imo.

• Fateslandia/Nolore: arguably an Awakening side story/sequel (prequel?) of some sort, especially with the 2nd gen trio in Nohr and the two clones in Hoshido. I'd like if they gave the continent an official name, but they can do that through other means (FEH, a manga, even just an interview...).

• Fódlan: we got seven alternate possibilities of how the story can play out here through the four original routes + the Warriors ones, enough is enough. Making a sequel is impossible thanks to the multipath system, and I'm not inclined to get a prequel.

• Elyos: I suspect this one is set up for a direct sequel like RD actually but who knows. If they do, I hope they severely improve on UI and QoL stuff because it was lacking in Engage.

TLDR: unless they do a giant time gap so it's effectively a new place, or a side story like Thracia I don't want it.