There are so many D&D locations even within the Forgotten Realms, and a ton of other settings with their own cool stuff. Why do another Baldur's Gate so soon? Taking a different direction might also blunt some of the inevitable criticism that it "isn't as good as BG3."
This is my biggest gripe with pretty much all official D&D stuff; it's always just somewhere along the Sword Coast. Explore one of the other thousand regions of Faerun that have some interesting premises. And not just Thay, either!
I'd love an open world Icewind Dale. A really, really complicated, dense open world with true mountain exploring and ice plain pain. Or, shoot, let's have an occult mystery in the city of Brass (Bronze? It's been too long, don't judge me).
Does anyone else remember Dark Sun: Shattered Lands? I used to play the hell out of that game. I love Dark Sun. It's such a great setting. I had the books, too.
Anyway, agreed. Dungeons & Dragons has tonnes of great lore and locations.
I'd love to have another campaign set in the Planescape setting of DnD, or the equivalent planar cosmology of Paizo's Pathfinder. Both are packed with unique and interesting places, races, and individuals. The cool thing about a planar campaign is that you can include a visit to the Prime Material (aka "normal fantasy") areas anytime you want.