After 16 hours my only gripe is that going back and upgrading old sections of my base is nigh unto herculean in work for what should be simple. Since sleeping quarters/sick bays always have to be an "end" and you want to use the cabins for maximum morale/sleep, plus the fact that the labs and other rooms have "wall mount" fixtures (so you don't want to be having too many connections) all makes restructuring painful. I just realized that if all my people zerged the food dispensers at the same time only about 2/3 of them can eat (long trade, slightly poor personnel AI), I thought I should readjust my food rooms, enlarge a few where there is easily space. Problem is, most of them have cabins (food + sleep next to each other seems like a no brainer) directly connected so for a room that has enough space to immediately expand I would have deconstruct both a cabin and the room, wait for the resources to be moved somewhere else or delete them, then drop the upgraded size room in. And that's for the simple ones. I also can't swap rooms with similar layouts (IE factory/robotics/processing plant or bar/canteen) even though the spacing and everything else is the same. You can claim design something something but if I were stuck someplace and had to build with sometimes limited resources, I think I would figure out how to make a bar into a canteen if I needed one more.

TL;DR I want sidegrades for structures and the ability to upgrade size in place if space permits. Also the ability to build internal sections separate from the main base (but not use until connected) for better base planning/layouts would be nice but really just the first.

I agree. One problem I encountered is when you replace, say, one medium structure with another one (like a wind power plant with a water tank), they sometimes don't fit the space. Maybe you shouldn't pack your base so tight.

Nevertheless the game forces you to think way ahead when designing your base. Structure prints would have been nice. Now, when I plan for future buildings, like a starport, I "build" it, then the structure i do want to construct at the time, then quickly recycle the first structure (so there is enough room later on)...

But maybe that is all for the best, the game would be quite boring if you designed your base from the start and let it all just play out... :->