I hope we get an in game event, perhaps they could have it so that we get the bottle by Wi-fi which causes a ring to form above Hoenn...perhaps over Littleroot with Hoopa inside.
I thought a number of the event Pokemon which show up in movies (so nigh all of them the last several years) have come out as either wifi or shop events across many countries outside of Japan.Since it's starring in a movie it probably won't be available through Wi-fi and instead be given out only to people who actually watch the movie, because the folks at the Pokemon Company think it's still 2004.
I'm not too crazy about it. It's alternate form looks cool, but battle-wise it doesn't look that interesting to me. I'll probably be more interested in Volcanion and AZ's Floette if they ever come out. As far as previous-gen legendaries go, I'd really like to see Jirachi, Darkrai or Arceus as Wi-fi gifts for ORAS.
I want to know what's up with Hoopa's Unbound forme, though.
He may be referring to how Hoopa is in the Kalos dex (while not being in the Hoenn dex) thus is a Kalos mon. Interestingly though Arceus and several mons from Gen IV aren't part of any regional dex...so therefore not part of any region by that logic. Though I actually think he is thinking of them as the way most mons are thought of when it comes to which region they belong to, in other words the region that was introduced in the same generation they were.
Anyways in response to the original poster, it's been done before. Deoxys was first available in FrLg not RS or Emerald despite being a 'Hoenn' mon.