It'll never happen. Hoenn is in Japan somewhere (at least the area it's based off of). X and Y are based off of France.
Also, Hoenn is not like the Sevii Islands added to FR/LG. It's a HUGE area. It would not become a secret area of the game. If anything, it would be accessed after the initial E4 run, and make it a 16 Gym game. For such a thing, they'd likely use Unova even though it meets the same reason I say Hoenn won't happen (Unova is based on New York, again across an ocean) - meaning I think neither will happen.
Cyclone