^I doubt they'd introduce a character on TV and then move them to the big screen. I think I saw an interview where Whedon or somebody involved with the show talked about why that would be problematical, because the stakes for casting someone in a movie are much higher than those for casting a guest actor in a TV episode.
Although, on second thought, we've already seen Bruce Banner and Jim Rhodes recast in the MCU, and will see Fandral recast in Thor: The Dark World
. So maybe a character could be introduced in the show and transfer to the movies, but the actor might not make the transition.