That's the great thing about it! When I'm buying coffee, who cares about decentralization? I just want it fast, and cheap so it makes sense to use the lightning network. But when I'm storing my life savings and transferring large sums, I don't care about fast and cheap. I care about secure and decentralized, so it would only make sense to use the Proof of Work chain. Lightning network wouldn't replace Proof-of-Work, it would simply exist as an option for use in certain scenarios. Do you see any potential problems?