But what if relays issue their own specialized ecash stamps? Users would purchase these ecash stamps from the relay using Lightning Network sats. 

Isn't this similar to an App coin? It's inefficient for every app to issue its own specialized coin; we only need a universal currency: sats. 

Relays should accept ecash sats issued by as many mints as possible and blacklist bad mints. nostr:note1re4sur0xjd8wxq0wqk8y5qjpp085kyqu7f5fe6zuz3p0e5kvrgfsxz4892