the point being that if others have time to shoot a movie, i'm sure joss and his schedulers can figure out how to shoot a tv series.
Plus, this isn't for tv. It would give them more leeway in terms of shooting.
Movie shooting is different than series shooting. An actor can do a movie project because it can be wrapped up in the off-season time. It's not impossible to do two series, but it's much more difficult than doing a series, then just popping in for a month or two on a movie.
Although that depends on how both the movie and the series is written/shot, if there's multiple on-location shoots, seasonal requirements, travel involved, it's even harder. Although IIRC, Castle is shot in L.A. (they do a pretty damn good job of faking N.Y.!) so unless they go to Australia or NZ for the tax breaks, or "otherworldly look" for some shots. Maybe it's possible.
Honestly though, despite how intense the fan-base is, I think Firefly/Serenity is a matter of "Too much time, too much water under the bridge, people have moved on." The best folks can realistically hope for is a new cast and TV show set in the same 'Verse. And then of course, it runs a huge risk of "Just not being the same", and dying all over again, since the cast is different. Maybe bolstered by cameos and walk-ons from the original cast where possible.
So for any new Firefly property that gets pitched, they have to be fairly certain they can hit the ground running, and hit some home-runs quickly to make it work and be worth the money and investment. Time is on their side for that. If a different story in the same universe is to be told, then the longer they wait, the lower the bar is. (Look how awful the first season and a half of STTOS was, and everyone still loved it...)
