Has Paizo ever considered an "Ultimate Urban" book? There really isn't that much out there about how to properly design a city top to bottom and then run a campaign in it. you could include things like a comprehensive list of the different shops and how to run them.. some advice on how to roleplay the blacksmith or the local magic shop beyond just stopping in, coughing up your 50 gp, and slogging back out to the dungeon/tomb/fortress to kick butt. I'd like to see a guide on things like how to properly design a tavern beyond just a common room and some bedrooms. expanded lists of equipment for procurement. some new subclasses based on an urban environment... really dig deep into city design.. how to lay out a city... what about the terrain it is built on? where does it get its water? is there a waterfall in the middle of the city with a hidden cavern complex behind it? what about how to lay out the different buildings... you could have a section of premade NPC's that could be dropped into a players city campaign. what about all of the different guilds? how do the religions play out in the city? do the evil cults slink around in the dark alleys to avoid the city or are they right out in the open?
for follow up you could do a set of pathfinder pawns for city adventures. miniatures. 3D terrain?
I think properly done you could easily get a 400-500 page tome out of the deal and I, for one, would gladly purchase it because the cities that are available for purchase are, in my humble opinion, not that well done. Typically, you get a map, that is of such high level it is virtually useless, a list of some NPC's of note.. a few adventure hooks.. and then they wish you luck. Not exactly awe-inspiring.
What else would people like to see in an Urban design book for Pathfinder? I'm sure I am missing a ton of stuff.