The tradeoff with this ofc is having to backup an additional piece of info
Can't you just use a bip85-like solution to derive a new "deterministic" mnemonic based on the nsec?
https://github.com/bitcoin/bips/blob/master/bip-0085.mediawiki
If the nsec has sufficient entropy then you can safely derive a new private key on a new hardened path and use that as entropy for a mnemonic.
Since this mnemonic is derived from the nsec, this could solve your problem I wonder?
Where am I wrong? 🤔
