There are a number of things that I would like to see, but if we focused purely on QoL fun gameplay. Midgame year needs more stuff for us to do that is actually fun, warfare in stellaris is pretty tedious. Endgame, we just need more stuff that does what the crisis does, where there are achievable win goals that aren't trying twiddling your thumbs because of the crisis war or waiting for the end game year to tick.
Actually, can I just say screw setups where you have tp pick an end game year and have no goals to work towards. I mean, I have criticisms about becoming the crisis being tedious but at least when I get everything in place I can end the game. I'm pretty tired of every update and every different built putting me in a spot where I need to trail and error stuff in hopes of getting good pacing that just doesn't drag on and I don't finish most of my games because the vanilla win condition does exactly that. It's rubbish design and I'm annoyed that the devs have hinted that they are inclined to do more stuff like become the crisis. NO, the game needs more win goals that we work towards that aren't dictated by some arbitrary year.