Dear god no.
Not at the Joss Whedon bit (though I'd hardly consider myself a fan) but the thought of Fallout as a film. They work wonderfully as games because they're ridiculously expansive with a narrative that develops as you wish it to. I've played Fallout 3 for about 40 hours and have done diddly squat in terms of central narrative, videogaming is the perfect format for it. If it had to be in any other form of visual medium then television would suit it best, but even then it would be too episodic, when what would work best is a constant sense of discovery with a dash of backtracking.
It's best suited towards videogaming, it isn't linear enough for film. Unless you want a 10 hour film.