I'm excited by the new districts, and as some others have mentioned here I think we're getting a good idea of how they work - with districts of a certain type that are upgraded as the game progresses.
I am concerned with what would be left of the
City Centre though, if everything is produced by the districts. Historically urban centres were incredibly important, so I hope that they remain useful/vital.
I'm also interested to see what all the 12 districts will be. I think we've seen (or can guess at):
Culture,
Science (although I hate the name Campus),
Holy Site,
Happiness,
Military Encampment and
Gold or Trade which is 6.
What isn't clear to me is if
Food is a district or a tile improvement (we've seen farms - but are these more like resource exploitation perhaps?), same with harbours/ports.
Hammers is the big one missing and I can see a lumber area in a screenshot so I wonder if it'll work like 
Pure conjecture here, but I think that districts will provide flat bonuses to their type, while buildings in the
provide % bonuses that exploit the region. For example, a Holy Site is founded with a Shrine that provides
+ 1 per turn when worked, and Monument built in the City provides a 10% faith bonus to the total
output of the City and it's hinterland.
That way the specialization of City & Hinterland takes place both in the districts and the urban centre, with the potential to adjust the specialization by knocking down Urban developments that offer one bonus in favour of another.
I am concerned with what would be left of the

I'm also interested to see what all the 12 districts will be. I think we've seen (or can guess at):






What isn't clear to me is if



Pure conjecture here, but I think that districts will provide flat bonuses to their type, while buildings in the



That way the specialization of City & Hinterland takes place both in the districts and the urban centre, with the potential to adjust the specialization by knocking down Urban developments that offer one bonus in favour of another.