Im thinking in the scenario of my existing browser extension, it works as nostr signer (nip07) currently it keeps you nsec, just like alby for eg. But with this nsec bunker, you would still sign in with the extension (nip07) but your keys would be in the bunker, not in the extension. If you don't want to use the extension, you can just get the nsec bunker string/npub and paste it the client. Coracle supports all of this is a good example. Ofc pasting your nsec bunker npub is not auto-login, it sucks, I think we could come up with a simple standard to make this auto fill automatic a bit like nip07.  

 Are you sure you want to auto-login into any web page you visit? It should probably require at least one click from you. 

 Yes, I said auto-login as in not having to fill anything, I also like it with a user action.