They never mentioned how Amon was able to take away bending, or who taught him, or if Amon was the only one who knew the technique. Whoever he learned it from, and how that originated would make a good plot continuation for season 2.
Spoiler!
Tarrlok implied that he used bloodbending to somehow "sever" one's ability (presumably).
Well, I think for the Korra movie, they would stick to animation. They were supposed to continue the other movie (so 3 in total) but everyone hated the first one so they discontinued it.