I wonder if most die hard Firefly fans are as anti-authority and anti-government in real life as Mal, etc (and me!)
We just watched Serenity (twice!). I think the series was better because it spent a lot more time on the character development and less on action.
A future Firefly series/movie could start right "what was that?" where the movie ended, or it could jump ahead months or years - the cast could even change somewhat. The Reavers aren't all dead and the Alliance isn't going to just ignore smugglers, but I agree they need some new problems to solve.
Heck, as far as I'm concerned they could crash land on some remote planet and spend the rest of the time playing cowboys and bad guys. Back at the Heart of Gold would be nice