Relatively new to Cosmoteer, but it's definitely something. This game and its current status as free and playable is like a golden hour moment in my gaming experiences. And I freakin' love it, so that's a plus.
I think about possibilities for the game often, which isn't uncommon. One of my common thoughts is multilevel (deck) ships. For example in the PC game cruise tycoon, there is a deck system for moving between the levels of the ship to access the buildable space.

I have seen this function somewhat in the parts galore mod where you can have roof mounted turrets/weapons, allowing for utilization of previously unusable surface for weapons and such. This was definitely something I enjoyed since one of the main things I think about in my designs is exterior surface usage.
So yeah, a mod that allows for multideck ships would be pretty rad.