Would it be possible (theoretically) to generate a npub from the seed and then have some kind of  nostr enabled version of ckbunker autosign psbt sent to the npub from specific whitelisted npubs and return signed transaction (for a multisig)? Like a nostr connected hardware signer? Or is this a dumb idea? 

 Yes, but could be tricky UX wise. Maybe on the EDGE firmware as it requires schnoor