I would be extremely surprised if it was possible to do a 4e retro-clone - WotC deliberately moved away from the OGL for 4e, and the GSL will surely be going away as soon as 4e ends (if not before). I would also be extremely surprised if anyone in my group would want to run a retro-clone of 4e, since those who I'd think might be interested already have the books.
However, my policy with any retro-clone would be the same as with any other game: if a member of my group wants to run a game, I'll play anything. (Yes, up to and including FATAL, if someone is foolish enough to run it.)
I won't run a 4e retro-clone, just as I won't run 4e; it's just not my cup of tea. But I have no problems playing.