Locking the Government behind certain Cultural paths feels underwhelming. (I started a new game as the Baratak Grove after purchasing the season pass only to discover that their Collective Culture path does not have special Government).

But I am not a big fan of choosing the Government right from the start. Unless I do some role playing, the Government depends on the galaxy map, opponents etc. I prefer the Civ 6 solution, where you unlock Governments in the mid early game through research. That way, one has a decent feel of the map and opponents and one can make a good decision. My suggestion is that the Government is either unlocked through Research and then "bought / activated" with Culture points (maybe with a discount depending the cultural affinity of the Government and your civilisation's affinity).

   Both.   Pick (unlock) the one you want to start the game with, then unlock the one you wish to change it to depending on how the game goes.

Question from the modding side: are the new governments data driven the way policies are, or is a lot of this hardcoded? Being able to define a custom government with its own screen and its own resource would open up a lot. If the screens are fixed then were limited to reskinning the ones that shipped, which is a much smaller sandbox.

Also curious whether the party and senate side is extensible or whether those lists are closed.

DST1348's point about picking before you have seen the map is the one I keep coming back to as well, though I land somewhere slightly different on it.

Committing at the start only bothers me when the commitment is invisible. If I choose a government in the first ten turns I am guessing at the galaxy, and a guess made with no information is not really a decision, it is a coin flip I have to live with for two hundred turns. That is the part that grates. Whether the fix is unlocking through research the way he suggests, or just showing me more about the map before I am asked to commit, I do not much mind.

The counter argument is that a start-of-game pick is a constraint you build around, and constraints are usually where the interesting play comes from. I play long games and colonise heavily, so by turn 150 I have usually made my peace with whatever I chose and shaped everything else around it. A mid-game switch would smooth that over, and smoothing is not always an improvement.

The locked-behind-culture part is the piece I would actually push on. Buying a season pass, starting as a civilisation you specifically wanted to play, and then finding its culture path has no government attached is a bad first hour, and it is bad in a way that has nothing to do with the design argument above.

Mid game unlocking would be worse for multiplayer, not better. If everyone can see the map before committing, everyone converges on whichever government is strongest for that map and the asymmetry stops meaning anything.

Picking blind is at least a real decision you have to play around. The season pass complaint is separate and fair though.

You can't add a whole new government no. You can modify those already in place though since much of it is data driven.