IGN:Filmforce has a rumour that Universal is planning a straight to TV movie sequel to Serenity. Joss Whedon's people deny the rumour. Which probably means that the studio execs are trying tom think of ways to squeeze more money out of Firefly fans and make more profits.
Personally I think that if Joss is involved it will probably be okay. And at the moment he's pretty busy so I wouldn't hold your breath.