I'm not sure on this, so correct me if I'm wrong, but I thought bank will only allow us access to parents for egg moves and hidden abilities. I dont think you'll be able to move a gen 7 Mon back to gen 6, give it a tutor move and then move it back to gen 7. I was under the impression that bank wasnt backwards compatible and you could only move mons to newer games, not vice-versa. Again, not sure, so I could be wrong.PokeBank is used to store pokemon from one game that you have (ORAS, XY) and move them to another. Right now, it isn't compatible with Sun and Moon.
Certain moves like Tailwind, Heat Wave, Hyper Voice, Air Slash, Defog, et al. were only available as TMs or Tutors in previous gens. When Pokemon Bank is updated, we can move those pokemon into our SM games.
This is what we know about "when".