If NIP-46 can be made more reliable, I am ALL FOR this onboarding flow. In fact. I would present the remote signing bunker string as, "This is how you log into Nostr apps. No email or password needed. Just keep this in a password manager and paste it into any compatible client. They will have it listed as signing in using a "bunker." Here's a list of clients:..." Then just give the nsec as a way to recover the bunker if it is compromised. Done.

This quorum of FROST signers is very interesting indeed! No single point of failure. However, it is still a relatively small group needed to collude, and I assume you need their cooperation to retire a bunker string, right? So if they DID collude, it would be no different from your nsec being compromised.