I don't  think this is a very good idea, although very content easy to manage.
I would drain the specialization of cities, and that would be sad. Btw how many level 5 cities do you have? am I one of few that doesn't take a trillion turns continuing researching more food per grain endless research? .

I think there should be more than 5 city levels though, since city levels are interesting, but the leap between each city level is huge and takes a huge invest, for a tiny little specialized building and 2 more gildar per turn.

But this is not a main issue, I would rather see a lot of other things be fixed right now, that said level 5 cities could use something to use food on.
TY for taking it up anyways, and making me think about it

Sincerely
~ Kongdej