Yeah, I've seen this twice. Already implemented in hosted channels and proposed as a way to allow people running multiple LN implementations to forward without having a channel.
New blog post: https://petertodd.org/2025/fake-channels-and-rgb-lightning
tl;dr: the fact that you can route over fake channels on lightning, means implementing Lightning on top of client-side-validated tokens like RGB is much easier than you'd expect.
Probably not a new idea. But someone's gotta write it down...
Discussion
To be clear, the (possible) innovation isn't fake channels. The innovation is taking advantage of them to implement Lightning on top of client side validated tokens.
Yeah, that might be interesting and I wouldn't be surprised if there are more interesting uses of fake channels. The issue is LN doesn't support them yet because, as you mentioned, it needs DoS protection.
Getting an alternative DoS protection would be great for privacy too.