2016 edit: This question is from 2014 and is outdated. Hoopa and Volcanion have both been revealed now and have had their own separate events. Click here to see Volcanion event dates, and here to see dates for Hoopa.
We don't know. We only know about these Pokemon because a hacker named Smealum revealed them along with Diancie last year (Diancie was also unreleased at that stage). Nintendo have not acknowledged the existence of Hoopa or Volcanion yet. So we have absolutely no idea when they'll release these Pokemon.
However, we do know that it is extremely likely that Hoopa will receive an event in OR/AS. A new form of Hoopa was found in the code of the games' demo versions by another group of well-known hackers. They wouldn't code a new form for no reason, so a Hoopa announcement and event seems very likely. We've heard nothing about Volcanion though.