Why would it be interesting to publish adventures and APs? This is exactly the market where Paizo deliveres in spades and then some. I fully expect splat books to re-emerge, especially as interested parties have had the alpha and beta rules for a long time and can publish such books in the not too distant future.
Adventures and adventure paths in
other publishers campaign settings (not the Pathfinder/Golarion setting) using Pathfinder rules. In other words, other publishers using the revised 3.5E rules (Pathfinder, developed by Paizo) for their own campaign settings and adventures/adventure paths.
I also think (like you) that Paizo makes some of the best adventures and adventure paths in the market. But Paizo probably isn't going to make adventures for other publishers campaign settings. IMO, Pathfinder Rules (and the Trailblazer add-on rules) allow 3.5E to reach it's full potential. And since, IMO, 3.5E was already the best rules system out there, this just makes it even better. I really don't think it's a huge leap of reasoning to want to see other publishers use the Pathfinder/Trailblazer rules sets for use in their own campaign settings and adventures. I'm eagerly hoping other publishers do just that.
As far as splatbooks, peoples definitions vary as to what constitutes a splatbook and what doesn't. For me, that's
"complete" books that simply attempt to make money by expanding on already existing material by adding extemporaneous material. For others, it's
any supplement other than the original core books (which by that definition would make Pathfinder a splatbook

). I tend to think that most people feel books they like, that they've added to their game, become
"core" for them - and
everything else are splatbooks. Your (everyone's) mileage
maywill vary.
I just don't expect a lot of
"complete" books based around the Pathfinder rules. Honestly, there are so many already out there for 3E/3.5E, that could very easily be updated by players and DM's for use with Pathfinder, that I can't imagine 3pp's would really be doing a whole lot of conversions. Also, with the economy the way it is, I doubt we'll see a glut or bloat for anything, including 4E, for quite some time. It's just the time we live in right now. Everybody is trying to think smaller and more efficient. Of course, I may be wrong about all of this (it has been known to happen

), but as with anything, time will tell.