But that's literally not how the lightning network works? If some intermediary in the chain wants to accept IOUs in place of real bitcoins that's on them, but on both ends you're putting in and getting real bitcoins. By "real bitcoins" I mean they can be redeemed at any point in time by closing the channel, and there's no risk of a bank run (at least to the sender and receiver). If some intermediary decides to accept IOUs instead of real bitcoins, that's on them if it comes crashing down.