You know, I've been wondering... I assume Mercer wants to explore a new continent as he is so engrossed in worldbuilding, however the remaining continents to seem a bit one-dimensional when compared against Wildemount. Plus, it would be weird for an all-white cast to play a game in Marquet, which is clearly inspired by the Middle East, or the Shattered Teeth, inspired by Asian cultures.
I then remembered this document the Mighty Nein found;
"I continue to find an aberration in my data pertaining to Exandria, a cyclical, months-long, slow surge in low-level magical interference that then recedes just as slowly. Something that tangles my readings and upsets my analysis. It is too faint to identify the arcane nature at source, but I worry if this pertains to to the shifting between the veils. It could be something very interesting. Something very frightening. Very wonderful. More tests are required." - Planerider Ryn.
It would be interesting if the next campaign wasn't on a new campaign at all, but started instead in a extraplaner city, essentially whatever Mercer's version of Sigil would be. From there, a lot of planar jumping, spelljammer stuff, etc.
Just an idea! They often do a lot of extraplanar stuff, but I found that quote above interesting, like Mercer was considering reformatting his planar map.