I have been mulling over my response to this topic ever since I saw the first post. I'm happy to see that Erik and James are here to see what we have to say, as well. Of course, they've always been awesome.
First: 1-20 can, should, and will be done. No question, as far as I can tell. Sure, shift "focus" toward the mid-level range, but an entire published campaign needs to take characters from low to high.
Second: Different minions. I understand the reasoining behind the use of fiends due to published material and room constraints. Perhaps an appendix now and again introducing a "new" creature that functions as a minion/fodder at the higher levels that can then be referenced multiple times, across multiple adventures?
Third: War. I love the war/invasion/Incursion angle. Political intrigue and would be easy to slip into such a AP, as well.
Fourth: Not (solely) Good v. Evil. I'd love to see some aspects of the AP deal with Law v. Chaos, Neutral v. Neutral. Country versus country, or somesuch.
Fifth: BBEG that is neither big, bad, evil, or a guy.

I'd love to see a LN or TN orchestrator of events. I'd love to see a Medium-size, normal person to be responsible. I'd love to see
multiple BBEGs with conflicting agendas.
Sixth: Plane/Terrain-hopping. I would like to see this, but with more variety. Arctic/desert/swamp/mountains/etc. would be great to see
all together in one AP. In addition, I'd like to see plane-hopping to places other than Evil Planes. Through in a couple netural, require a visit to a "good" plane with goals, though not counter to the PCs, at least not completely aligned.
Seventh: Elementals. I love 'em. Maybe not the Princes, but I would love to see the variety of them that can be used (wierds, arcane casters, et al.), especially as troops in a magical war setting....
Just some of my ideas. Thank you, Paizo staff, for listening!