I hope that whop ever reads this, the day/night finds you well.
First off, I haven't been playing it very much until lately, now that I have been playing it longer and longer I have started to notice a few things that need improved as well as some things that would be nice to be implemented, so here I go.
1. Colonize Nearest command would be great, I've gotten tiered of telling every single colony ship to each planet.
2. Module Viewer, This will allow you to view every module in the game, Weapon wise is mainly what I am looking at so you can see how it looks when firing and when hitting a target with or with out the defense for it.
3. With the suggestion above, it would be nice to be able to add in game, a way to change the skin and the weapon effects to another weapon type for more added cosmetics.
4. Bring back the tech, building and module editor/creator from GalCiv II back, please! 
5. When colonizing a planet, it would make more sense that there is a ring around the colony it self, then anything else is extra space to build in, if it was me personally I would pick a place with a lot of building space around the initial colony.
6. Contested or partial ownership of planets, Where you can invade a planet and have a on going war on the planet or even give half of the planet to another player to avoid total destruction of that player. (tho sounds cool, this isn't likely gonna be possible.)
And well that is about it for now, maybe I will update this later with more ideas or comments, Thank you for your time in reading this.