I still love Civ IV's way of dealing with ICS...and so I instinctively like this suggestion.
The Civ IV system was pretty good gameplay-wise and explainable flavour-wise, I agree. However, it feels much more like an in-the-way thing than the scaling district costs do. I've never been like "oh no I need to be careful my districts don't get too expensive" while in Civ IV you're constantly thinking "okay, can I build that city now or is it better to wait for a bit so I don't have to put my science rate down to 50%". It's a system I can't critque a lot, but the increasing district costs are "smoother", I guess I would call it. Can't really put into words how it feels, but I like scaling district costs more than maintenance costs.
What? I'm talking about from a games mechanic standpoint. In past Civ games there were no districts, just buildings, and districts are just buildings that sit on tiles.
So in your eyes, a district is just, as mentioned earlier, a zoning tool?
I mean, that's fine, but it's not how I view districts. I would say that placing the district also includes building roads, shops, sewers, you know, everything that you need to get a place running. And the amount of things you need to keep a place running, as mentioned before, increases with time. In the ancient, classical and medieval era, there were, for example, no sewers (excluding some empires like the Roman Empire, of course), maybe not even the renaissance yet. As for electricity, it wasn't until late industrial/early modern era that it was introduced. Etc.
As mentioned earlier: scale the cost with the number of a particular district in your empire, scale the district cost with techs that actually boost districts, scale the cost with time. Some of these solutions aren't ideal (I think a flat cost is better), but they're better than what's currently implemented.
Scale the cost with number of a particular district in your empire: An understandable choice, most certainly, but this strongly pushes you into building a few of everything, and on top of that is probably the hardest to explain flavour-wise. Additionally, it discourages pursuing a victory as it will feel very annoying if you just want to focus on, for example, a Culture Victory, and are trying to get all those Theater Squares up as soon as possible, and by the time you have five of them placing down another one will cost 80 turns - and you don't yet have a lot of trade routes, nor is your city going to double it's production by growing from size one to size four, as it's already size five.
Scale the district cost with techs that actually boost districts: I'm sorry, but not a page back this has been explained clearly by someone else, it doesn't work. It means that you have what, five or six times the district cost increases (or do you want them to triple in cost every time?), times
twelve districts, meaning you have 60 of your combined ~130 techs and civics (do we even have that many?) that give a cost increase, every second one of them. On top of that, it would mean things like "it's actually best to delay education if you're going for a lot of science, as your campuses will get more expensive once you get it" instead of "yeah, district costs rise as you advance through the ages as they get slightly higher every time you research a tech or civic". Making it scale only with techs that have a relation to the district gives you sudden bursts of price increases which are either played around with annoyance or not played around and being met with
more annoyance, while making it scale over time makes you not care (too much) about the price increase as it'll be there no matter what you research first.
Scale the cost with time: I'm pretty pretty sure I've explained that in the post I made before the one you're currently replying to, so one time my post up in the quote line. Starting from "districts have to scale during the game" (which is a different discussion from this one), if you choose between making them scale with time or making them scale with techs and civics, then making them scale with time hurts civs that are behind in favour of those that are ahead - not to mention civs that are eliminated and then get liberated - while making them scale with techs and civics actually slightly help civs that are behind (comparatively; it's quite possible of course that the civ ahead still pumps them out faster because they got Apprentinceship or Industrialization or just bigger cities or whatever). In a game like Civ, where being ahead in and of itself is an advance simply because you keep unlocking more and more as the game progresses, it can't hurt to have a few mechanics that keep the snowballing in check. The game snowballs naturally, and certainly doesn't need help doing so.