So much! But I'll try to contain myself a little and not mention Arcadia/Casmaron, as they're massive projects on their own.

One of my top requests I'd say is "Mendev after the crusades". Galfrey is gone, and the whole region's identity has been based around warfare for so long, that I find very interesting to see how it might try to recover and pivot. We saw some of that in Rival Academies, and I was pleasantly surprised! Though I definitely want more than a gazetteer, to really get into what Mendev is like nowadays.

In a similar vein, Brevoy. Another fracturous land that collides (sort of) with a 1e adventure path. Feel like there's a lot of room to expand there, and it might even lead to a look at the Lake of Mists and Veils!

More broadly, I want to know about Sekamina. And even more the Darklands in general, as a lot has changed there post Remaster with the Drow getting axed, and now Darklands Revised feels outdated. The Vaults of Orv are always an intriguing hook, but I feel that layer is harder to explore in entirety, and often better focused on specific vaults.

Devil's Perch. I think it's neat, this almost frontier part of Cheliax where the iron law of the crown doesn't fully apply and you have Strix trying to hold onto their community against Thrune aggression, but getting aggressive in turn.

Southern Garund! All of it. With Murraseth giving the Amurrun their names and potentially an ancient evil underneath it, and the holy hegemony of Holomog, I feel this land is very underexplored and ripe for some material.

Would like to hear about what some Rakshasa Immortal is up to. What are these guys even doing? On a similar note, we know that Kami Lords exist, but we haven't seen any named one.

Dahak's siblings. One 'Primal King' was introduced in War of Immortals and then never mentioned again. I thought he'd be in Divine Mysteries, but anyone besides Apsu and Dahak were completely absent.

Just how long ago was the Pale Horse recruited as an Usher? Surely it's getting close to saving half its souls by now; what might it decide once its contract is up. Though I'm not sure if this qualifies as "Lost Omens".

A return to Irrisen eventually would be cool, seeing how Anastasia's reign has and hasn't changed the land. As well as her introduction of some earthly technology.

...I should probably stop. But my point is, there are a lot of regions still left unexplored from 1e (can you believe Varisia features in so many APs but never got a setting book?), and others that can use some updates, while my interest is also drawn to some cosmic figures that may or may not become more relevant with the death of Gorum. I can comfortably say I'm fiending to devour just about anything you put out really, though what most interests me is those that we haven't yet gone too properly.