Michael Madsen did an interview last year that stated Tarantino has an idea for the prequel that is doable considering they are both atleast 10 years older than they were in P.F. and R-Dogs. Madsen also mentioned that Tarantino wants to finish the project he is currently working on so it would take atleast 1-2 years.
The film is supposedly going to be about the Vega brothers running a bar in Amsterdam. Remember in Pulp Fiction Vincent is always talking about Amsterdam, so the Vega brothers movie would be set just a few years earlier that P.F.
I think this is one of those films they really want to do, but considering the age differences, how are they really going to make a prequel? I mean have you seen Madsen lately. He unfortunatly doesn't look nearly as young and hot as he did in R-Dogs. Same goes for Travolta. So how can a believable prequel work?
Basically the movie is great in theory but could suck in actuality. Personally I would love for them to do it. Travolta and Madsen are great actors and I've loved everything by Tarantino.