Why shouldn't an outpost cost maintanence? If all it is is an outpost with no infrastructure of its own, it would logically need to import all of its supplies for the small number of people living there.
what I suppose I mean is that an outpost (level 1 city) should only ever cost 1 gold in maintanence, and not be included in the official "city count."
If our "actual cities" are going to cost ever increasing maintanence I would rather it be an additional sequence.
What I mean is, that if you have 8 cities, your city maintanence would be 8+7+6+5+4+3+2+1 + Xoutposts
In that case, the amount of cities beyond level 1 would seriously allow your maintanence to add up. In this case, city maintanence would be 36 gold per turn for only 8 cities, and if you had 8 outposts AND 8 cities you would have 42 maintanence per turn. If, however, you upgraded those 8 ouposts BEYOND level 1, and they all became level 2+ "cities" at least in the official city count, then you would have 16 cities, which would be MUCH WORSE than double the amount of 8 outposts.
16+15+14+13+12+11+10+9+8+7+6+5+4+3+2+1 = 136 gold per turn. That would be alot worse, than say, having 8 cities (36 gold) plus 36 outposts (+36 gold) = 72 gold. Having 16 cities is almost twice the Expense as having 8 cities and 36 level 1 outposts. See ... this is what I mean by little-no maintanence, what I mean is that owning More cities means that your going to need to be making even more money than would normally be required. Therefore you can have a large merchant empire, or a smaller specialized empire. Personally, I think this Idea is full of win. I also think that level 1 cities should only be able to build Huts, Walls, and Resource Gathering Improvements. I also think a level 1 city should be able to "send" the entirety of its resources to another city its connected to for a "travel fee" of 1 gold per turn.
In this way, you can have a hub of resource collecting "outposts" (level 1 cities) each costing 2 gold per turn at no additional fee. Say you have a Hypothetical resource accolation of 12 outposts or 6 cities to gather the same amount of resources. Lets also say that theoretically, if you could send all of your resources to your Capital (instead of sharing among 6 other cities) it would aid you Equally (or even more-so, cause extra cities might still mean more building room).
In this case, you can either spend 24 gold per turn in maintaining Resource Sapping outposts (sending the ENTIRE resource output to one city) OR you can spend 7+6+5+4+3+2 = 27 gold per turn using your additional 6 cities.
of course, this is Empire Wide city maintanence. So lets additionally say that, before deciding to mine this lush Region of its resources, you ALREADY had 5 cities. Which is a reasonable number. THEN the "larger" city option would actually cost 6+7+8+9+10+11 = 51 gold per turn VS the 24 gold per turn if you used Resource Grabber outposts.
In this way, your Empires and Kingdoms would organically build cities around the nearby resources which have enough land and food for large cities, and the smaller, crappier resource sites (like an Ore or a Shard in cramped quarters) can remain a simple outpost, with little comparative long-term expense to the player.
Additionally options to both Raze a city completely (which should take multiple turns for high-level cities) or for simply burning down buildings and exterminating population to bring the City level DOWN (during wartime).
A peaceful option would be to decommision buildings by way of Royal Eviction notice, and to FORCE migration from city X in order to demolish it with no colateral damage (all about maintaining/organizing your empire). In this way, you can peacefully remove unwanted cities, or reduce unwanted cities in size and population to that of an outpost. However, you should need at least 66% or 75% influence over a city to peacefully decomission cities, so it shouldn't be possible to peacefully destroy a newly captured settlement.
I think this would vastly improve how all players, human and AI, manage their Nations. Unless a similar idea is already planned for implementation.