So, I was thinking about autonomy, right?
As it is, the further from the capital and the higher the population, the faster autonomy grows. The higher autonomy gets, the lower unrest gets. And low unrest reduces autonomy growth, eventually leading to equilibrium.
Except, said equilibrium involves an inordinately happy province. A province halfway round the world may have 100% autonomy, with people openly flaunting their defiance of central authority, but it ain't never gonna rise up in revolt, cos at 100% autonomy its unrest will be incredibly low. (It will also produce bucketloads of ideas, and make the owning faction even richer due to high A/U/GE)
I'm guessing this is not the intention; it seems to me like provinces with high autonomy should, if anything, be more likely to revolt. At the very least, their unrest shouldn't be significantly lower than any other province.
I have a suggestion for how this could be avoided, though I don't know how feasible it is.
Instead of distance & population increasing the rate that autonomy grows at, they increase the 'target autonomy' for a province. Target autonomy is the autonomy level at which autonomy has no effect on unrest one way or another. Below that level, it increases unrest, and above it, it decreases it. High unrest will still increase autonomy growth (and low decrease), leading to the same equilibrium, except that unrest will be ~0 (before other modifiers).
I'm not sure whether decentralisation should decrease target autonomy or autonomy growth; either way stable autonomy is lower, but if the latter, provinces would also be less happy. I would lean towards effecting target autonomy, since most people don't get upset if you give them more control over their lives. I feel like Autocracy should decrease autonomy growth (and thus happiness)(people don't like living under a dictator), but maybe for balance purposes it should affect target autonomy instead.
There would definitely need to be some ways to decrease autonomy growth, leading to unhappy but obedient people. Law&order buildings, perhaps? Dungeon, courthouse, governor's mansion, etc.
Edit: Actually, thinking about it some more, that would always result in unrest trending towards 0, unless autonomy was at its minimum, in which case unrest could drop below 0. Hmm. Maybe just forget about autonomy growing/shrinking, and just have it immediately reach its final value. Unrest would still have an effect on autonomy, but not vice-versa. I mean, having autonomy grow slowly over time is cool, but is it worth the bother?