Hi, thanks for the suggestions!
1. I guess a faction could change the government type perhaps?
2. What do you mean fixed empire scale, you mean you would prefer to block new empires? You can just create the world as you like it and set the limit to 1 in that case, nice trick :)
3. I've definitely thought about making an entirely new game for that (codename Planimulator) - but nothing concrete on that. It's very big change!