A better way to frame it instead of one user per project, is to have one persona (casual me, working me, planning me) per workspace, each of which can only be used by one identity on the whole machine.
lol, I wasn't framing it in terms of users, it was just that you could corrupt fast user switching, which exists, to be fast project switching (which needs to exist).
Multiple desktop shell sessions per user. Oh yeah, that would rock