I don't think the solution is one thing. I think it's many things. Liquid, mercury, ark, lightning, fedimints. All solutions. We should not be afraid to explore them all.
Discussion
All of these are already working on using Lightning as an interoperability layer, unfortunately.
If we're not careful, lightning will be to #bitcoin how JavaScript is to the web.
Imagine if Bitcoin could do this. It can if we allow it. Nostr would be insane.