Another aspect I don't think we've touched on yet is I love city builders which have an aspect of cleaning up the map as part of the expansion process. Rebuild and Rebuild 2 are some examples of this - they are zombie apocalypse games where you are retaking a city piece by piece from the zombies - sort of a city-builder hybrid. And a lot of games have piles of rubble or thickets that need to be cleared away before you can build there, and give the player some kind of resource or chance for a bonus item in the process.
I think it's a 'Burgh thing. Urban reclamation is our fundamental narrative :)
I want a city builder that naturally leads to player-generated stories about cities. Each city has a history, and that history has led to the city having something of a personality; a city has character. And just as with people, that character evolves over time. Neighborhoods within the city likewise have character and histories.
That is a really interesting idea. I'd wonder how to get this kind of character out of a game.
So part of the character of my hometown is that there's a LOT of reclaimed architecture, and it's pretty common to find civic and private institutions in former factories, mills, churches, etc. But everywhere has that to some degree. (Hence: http://usedtobeapizzahut.blogspot.com/.)
That's a key part of local character but not something I can recall ever being in a city builder. When a city-builder building ceases to be it either decays or disappears or kinda decays then springs back as the same thing. You don't end up with restaurants in old warehouses, churches in old restaurants, university dorms in old monasteries, and all the other stuff you actually find in cities that gives them some history.
This wouldn't be a walk in the park so far as art & programming are concerned, but it's not impossible either. You'd want to plan ahead so that "new owners" could slap on a new coat of paint and some signage, maybe subdivide or build annexes if the new usage takes up less or more space, add a parking lot or a drive-thru, etc. And not for every building -- you can't reasonably make six houses into a grocery store, it's better to tear them down. But having a bit of procedural architecture that can adapt buildings to new uses would go a long way towards giving your cities realistic character and a sense of having a narrative.
Related: R. Crumb's classic illustration A Short History of America: http://www.wired.com/images_blogs/beyond_the_beyond/2013/08/SHOA.MED_.jpg