You keep saying "no protocol changes required", but then propose a bunch of protocol changes (yes, new tags and client recommendations count). I'm also confused by your use of "deterministic", are you using HD keys or adding a link? the latter isn't deterministic, and HD keys don't really work for this (blinded addresses can't be linked, and compromise of an unblinded private key compromises the root).
Are you familiar with NIP 26? That was basically this, but was never adopted except by Minds because of the complexity it imposed on clients. This approach also only works for people who understand cold storage and how to safely derive keys, which is ultimately going to be a very small minority. It's also helpless against key material loss, or an attacker getting the root key.
A few weeks ago a group of people were able to meet in person and talk through this problem (from admittedly a different angle). We came up with this:
This allows for making your root identity disposable by advertising a migration event based on a precommit that an attacker can't get access to. It's better I think, but of course there is really no silver bullet in this domain. Everything comes with huge trade offs.
GitHub
Key migration by staab · Pull Request #2137 · nostr-protocol/nips
This NIP was sketched out in a session at nostr.xxx. It's based on @pablof7z's original migration proposal with some elements from #2114.
D...