There is a E to Z adapter….so in theory maybe an RF to E adapter is possible. Might be pretty tight towards the grip though, given the girth of RF lenses towards the mount (due to the diameter of the RF mount. Given that E is narrower than Z, it’s seems like an easier mechanical problem to solve than RF to E.
From what I heard, it might not be possible because the RF lenses go inside the body quite a bit, and that the flange distance isn't necessarily the only concern when it comes to adapting RF lenses to FE.
However, I can't see why you couldn't develop a lens adapter for lenses that are also made for Sony FE. The reason why I want this is that I have both Sony and Fuji cameras both with about 16mm flange distance, it would be nice if I could use a RF manual focus lens on both of those camera systems.