Ya you just go into read only mode with their npub but there is no logging in or out as in a typical log in form, you just “assume their identity”. I think some clever transition and css effects might give it a special feel. I’ll play around with a mock-up.
Discussion
I've just deployed a new nostr-login on nostr.band (reload hard please) that has account switching. I've got my real key connected, and also jack in read-only mode. Switching is a couple of clicks. Nostr.band doesn't personalize the experience much, but the concept is working. Switching is log out and in though from app's pov, so it might be heavy depending on the app.