For one, UI/UX is actually hugely important for a consumer device and definitely nontrivial

Hugely agreed. I’m a huge proponent of DIY / open-source / self-hosting / repurposing etc…but also I realize if I duct-tape-engineer something that “requires a little fiddling until it works” and I’m the only one who can competently use it, I’m setting up the rest of my household for failure when (not if), for whatever reason, I’m not there to babysit it or walk them through it.