Oh, wow, all members are on one page as a matrix? Sorry, didn't realise that (I don't admin any communities). Suspect that's unwieldy even at present.

So, take my thoughts above, and add at the top a proposal that only one user's permissions are edited at a time. This would get tedious if a lot of users were to have permissions, hence my thought about introducing a "roles" system as another layer.

Hope that's clear, but I'm really tired, so please ask for clarity if not ☺ (and if you care!)