1) My first choice would be monsters-as-PCs, but I don't think that the Pathfinder folk are going to be any better at it than the WotC folk, and come up with some lame kludge like the Complete Book of Humanoids or Savage Species or 'racial levels,' instead of having done the ground work to make the Bestiary beasties function alongside the PC races. Since that wasn't done, any sort of Pathfinder 'serpentfolk as PCs' rules will be equally borked from the start, IMO.
2) An Asia-esque setting book would be neat, but, again, I have all the 2e Kara-Tur stuff (and 3.5's Oriental Adventures, set in Rokugan), so I don't *need* such a book immediately. Given my love for Kara-Tur, I'm not sure if any attempt at creating yet another pseudo-Asia is going to satisfy as well, and I'd buy such a product just to see new Domains, Bloodlines, race options, etc. 2e and 3e's Oriental Adventures settings did one thing wonderfully, and that was to turn the Monk class from a neglected bastard step-child to a thing of deadly beauty. The Pathfinder Monk is less dire than that d4 HD 1st edition afterthought, but I'd be interested in seeing what sort of new feats, class options, ki powers, etc. could show up in such a product.
3) Psionics are already part of the setting, thanks to the references to Vudra (then again, so are guns, thanks to Alkenstar), and, IMO, I can either use the 3.5 Psionics rules, tweaked slightly for Pathfinderization, or Green Ronin's Psychic Handbook / APG rules, similarly tweaked. I don't really *need* official rules for psionics, but I sure wouldn't mind them.
I have less than zero use for Epic stuff, but other people like it, so they would be well-served to make it for them. Similarly, I've got no use for Modern rules, or Sci-Fi rules (although a Spelljammer-esque setting that explores the other worlds of the Golarion system could be all John Carter sword-and-blaster goodness!).
So, my priority list
1 - Monsters as PCs
2 - not-Asia
3 - Psionics
4 - Sci-fi
5 - Epic
6 - Modern
Somewhere along the lines of 'not-Asia,' I wouldn't mind seeing 'not-Persia' and 'not-India' and 'not-Africa' sections fleshed out, similar to Al-Qadim / Zakara and Green Ronin's Mindshadows / Naranjan and Nyambe. On the other hand, I can just as readily strap Zakara, Naranjan and Nyambe onto the world of Golarion, the same way that WotC strapped Zakara and Kara-Tur onto the Realms (Zakara to the east of Qadira, Naranjan further east yet, and Nyambe-Tande south of Mwangi). Seems like a potential waste to not use the awesome setting material I already own, until Paizo gets around to fleshing out Vudra and Casmaron, after all.
I sure won't be doing that with Maztica-in-place-of-Arcadia, 'though. Ugh.