Another alternative, that I'm testing right now, would be to reduce max tax rates from 90% to 80% for Federation. This way:
* Since AIs like so much this government, they would be forced to set science to at least 20% (double research).
* It might encourage some AIs to change to Democracy if they want 90% tax rates.
* Democracy has less chances to become obsolete by Federation, even when the tech tree is finished, or corruption by distance is high.
Related to #42078
In that ticket, the op pointed that AI uses to prefer Federation over Democracy, while Republic is hardly used by the AI. It is also this way in my tests. Also, in oceanic/island maps, Federation might be better than Democracy to produce science even with small empires (and low distances).
I'm thinking that we could use the new feature from 3.0: Output_Waste_By_Rel_Distance If we use this distance, relative to map size, for all governments, it will be easier to balance them when compared to governments with no corruption by distance (Federation/Communism), and the balance will remain no matter the map size: the max corruption in a city will be the same in every map.
In the other hand, when the distance is relative to the map size, the corruption/waste in the initial stages of the game will be different depending on the map size. For example, when you have 10 cities, the distance (number of tiles) to the capital will be similar, but the corruption caused by that distance (relative to map size) will be higher in a small map and lower in a large map.
I'm not liking this part that much, and I wanted to hear other opinions. Anyway, such change would require lots of testing, so no plans to make it anytime soon.