This is also my answer. Anything I do, usually will by done with this nym/keypair, but I can see needing to test with a new npub or checking out a new relay with a "burner" before committing to something with my main nym.
Discussion
The challenge has been allowing anon writes and then immediately displaying them, without it turning into a gross thread, but zap-to-write helps solve for that.
I actually use npub login a lot, as it has a more persistent session than Amber, and I can just anon-zap or upgrade to Amber, when I want to write.
Was thinking, I could have broken Amber sessions fall back to npub-only, and just give them a message that they'd have to reconnect, to write.