"emerge lufis" doesn't require lufs as a dependency, as it should.
Why should it? lufis is an API-compatible layer for stuff to interface with fuse. lufs is kept out of the equation, if my understanding is correct.
mmmh. you're right, I didn't think that one could write a filesystem for lufs that is not included in the lufs package, and then want to use it with fuse. /me definitely too tired -_-'''