Yeah, that sure would've been interesting if FM continued with Billy & RV, BUT it really only would've "gone anywhere" if Billy & Rick were "allowed to be themselves" (musically speaking) in FM and I get the feeling they weren't allowed to do that (at least by listening to (or in my case reading about) what was actually released and what wasn't) and I'm guessing the "creative/musical differences" reason, though overused etc. is at least partly applicable to why (at least RV) left though I guess we'll never really know the whole truth behind that since there must be much more to it than that if even Rick won't (can't?) talk about it as we know how nice and willing he is to communicate with fans etc.) unlike others.
With this being the case, I think we would've just gotten "Behind the mask 2" from the "powers that be" (which I'd enjoy I'm sure but I don't think Mick's "holding back" tendencies are what Peter Green would've liked (if Mick was continuing the "spirit of FM" that he probably thinks he is/was). JMHO though.
John