Welp. · 3:34am Feb 6th, 2018
Installed every update. I got on to the final update that was supposedly marked as "Important", which was Windows RT 8.1 Update 3. Turns out it's actually an optional update that the Surface RT somehow mixed in with everything else, aaaaaand... the whole thing bricked again.
Another reset later, and now I'm going through installing updates for the third time now, and this time, I'm gonna pay special attention to what's installing and what isn't.