Now that we know that patch 4.3 will be the final Cataclysm content patch and contain the means with which to kill Deathwing, we know beyond reasonable doubt that epic gems will be released in that patch.
It's unreasonably doubtful that Blizzard would introduce epic gems before 4.3, and aside from not introducing epic gems at all, that's the only option that would lead to my prediction being wrong. That said, there's tons of stuff we don't know about how this will work. Here's a big one: Where will epic gems come from? If we knew that, intelligent auctioneers would start stockpiling ages before the patch in preparation.