Almost certainly not. It only happened between Gen 1 and 2, and it has never happened since. If they let us transfer from Gen 5 to 6 (which they probably will) then it will very likely be one-way and permanent.
I just realized that you were asking about new Pokemon. If they let us transfer from Gen 6 to 5, we definitely won't be allowed to transfer any new Pokemon or old Pokemon with new moves and abilities, since the new stuff doesn't exist in Gen 5. Gen 2 didn't allow you to send new Pokemon or Pokemon with new moves back to Gen 1. --- Official Nate of the Pokemon X board with my pet Medicham and Victreebel 3DS FC: 3609-1237-6725
Wait... I'm not sure what you're asking. Are you asking if it's going to be possible to trade gen 6 Pokemon onto the gen 5 games? If you're not... I must be reading your post wrong. --- Let's just pretend this says something witty.