How would it work, even if they Do it with two DS. You can't just have it transfer from the one, wirelessly, or something. You could probably steal peoples pokemon, that way, by transfering them when they weren't looking, lol. I'm thinking Time Machine.
How would what work?
Time Machine? Same way it worked in R/G/B/Y to G/S/C. In the next gen, you enter the time machine, but you can only bring in pokemon, items, and moves that have existed in the previous gens, and just trade. So no new pokemon, items, or moves.
Oh that time machine, I thought you were talking about something else. But like I said before, theres no need if they keep remaking the games.