Think of this. Currently if a new player managed to get resources, or use creative to build a large ship on their first week into the game, where is the challenge in designing that ship? If they aren't expecting combat
Salvaging isn't so simple, as evidenced by the multple "how does salvage work" type threads that pop up in general. Yet a "good enough to get started with" one isn't hugely difficult, i was mining good enough to have fun within the first few hours of picking up the game, but built a new salvager a few months ago, which i am again planning to replace soon, why? because i learned how to make a better one with fewer beams, thats a couple of years for me, maybe a couple months to a year for a less slow person to be fair, not so simple. That's one example but truth is there's not a lot of non-combat options that aren't RP focused yet.
As far as adding depth & complexity to more RP focused vessels, we kinda have no features implemented for that, unless they pick some kind of engineering theme that actually exists in the game and not just "i want this super high tech reactor room with a beautiful & techy lookin reactor made out of ice crystals and pipes actually give me an advantage", and i'm not sure that's all that fair on the other kids in the sandbox anyway. Every ship is intended to at least function, unless its intentionally built to be non functional, in which case they can't complain when it doesn't.
What kinda non-combat ship being designed, if it's actually intended to function, would have no challenge to build and improve upon? I really can't think of one right now other than a 3 block core-with-thrust-stick, after all it doesn't only start getting hard when you start adding weapons blocks, I've seen functionally focused salvagers as complicated and "deep" in design as any pvp ship, and to be honest it's a credit to the game that a beginner doesn't have to throw themselves straight into full gyroscopic turrets, docked hulls & effective hotswapping set-ups just to build a simple freighter and get out of 2,2,2 for the first time.
well i planned like one sentence there, and got a bit more wordy, but tl;dr is that i don't think non-combat designs are so simple, they can be as complicated as combat ships just without guns in them, it really depends on the actual focus, and if thats "looking awesome", while not a super practical focus (unless you add an awesome-to-power convertery thing) it can't be said to be not-a-challenge can it?