Bitcoin seeds (when stored well) are much more secure, assuming they’re offline.
Nostr keys are “hot” in pretty much every circumstance. Perhaps there’s a way to generate a nostr keypair offline with dice (I have no idea) or with a HWW-style random number generator…? But even so, it would need to be able to sign so many activities on a regular basis…
But then again this gets me thinking - a personal “yubikey” style nostr signing device for most digital activities. You could choose to have multiple if desired. It could serve as an ID (for work, or apartment access, etc.), or it could be anon and used for payments. Or any other permutation. It’s an interesting idea.
But your initial question was about a universal *client*, not a universal keypair, which comes back to the issue that if the client is compromised, your keys might be too.
I.e. your seed phrase is fine in your coldcard, but if you import that seed to BlueWallet and then your phone gets hacked, bye-bye money.
Ava, I’m curious to hear your perspective - “honey pot” was your first reply, & you’re the cybersecurity professional, not me 😉