I like the idea, interesting to think about. Simple enough to get widespread adoption:

If you have "proof of stake" in a BTC wallet, lets say 100ksat, then sign your npub with the wallet private key and post the pubkey and signed message to your profile, then if someone steals your nostr nsec you can sign a new npub with the same wallet, then your identity follows your cold sats rather than an nsec that has to be hot.
If you want to shut down your profile, just spend the sats to another wallet.

If an identity misbehaves, you can ban the wallet address so they can't just create a new npub and keep spamming you. If they move their funds to a new wallet, well then they just paid a transaction fee to create a new identity.

Now your client and/or relay can set a "minimum identity stake" so you only are talking to people that are serious.