Isn't that a bit insecure? Nostr users are relative fast to enter their nsec into new clients. If the key now also gives access to your bitcoin, I'd expect malicious clients to appear very soon.
Smart Vaults for Testnet Available on iOS Testflight
"Smart Vaults are miniscript-based, P2TR Bitcoin wallets that use Nostr to coordinate metadata and PSBTs. Users create a single “account” (mnemonic) with the mobile app, and that key is used for both Nostr events and Bitcoin transactions."
https://www.nobsbitcoin.com/smart-vaults-for-testnet-available-for-ios-on-testflight/
Discussion
This nsec would only be used with smartvaults I guess