I agree. I'm not saying you would do that. I'm saying you could:
1. Generate an nsec from your bitcoin private keys
2. SEND to any nsec if you wanted to. (the receiver would be highly encouraged to send to a real bitcoin wallet after receiving if someone sent them something)

#2 is basically moot if #Nostr contacts are integrated into wallets, because you can have the clients communicate to get payment details if desired.

I'm not suggesting to advise people to generate a #nostr ID and then use that as their bitcoin wallet keys. I'm just explaining that the standards are exactly the same and the UX could be vastly simpler than we currently have it across the ecosystem by thinking about it this way.