Are there really people still talking about epic gems? Apparently so. Let me make it really easy for you: epic gems will be released when all the profession bonuses are updated.
The stat bonuses from any one profession is around ~80 extra stats above what you could otherwise attain. As you can see from the pictures above, a Bold Chimera's Eye grants +67 Strength vs a Bold Inferno Ruby with +40 Strength. (67 * 3) - (40 * 3) = 81. Mixology from Alchemy increases your flask strength by +80 stats, Synapse Springs gives a 480 stat bonus for 10 seconds every minute which is a ~16.66% uptime that averages into 80 stats, and the wrist enchants such as Major Strength were expressly added into the game to counteract imbalance that came with Leatherworkers having Embossments, such as +130 Strength, when everyone else had to settle for +50 Hit or +50 Haste (nevermind how much better primary stats already are from secondary ones this expansion).
If epic gems were added to the game, the profession bonus for JCs would diminish from 81 to 51, assuming that epic gems are +50. Simultaneously, the profession bonus for Blacksmithing (two extra sockets for +40 gems currently) would outpace everyone else as they are able to fit in two extra epic gems. Clearly, this would be bad design. The imbalance was fixed in Wrath in patch 3.2 by increasing the stats on the JC-only gems, keeping them proportionally as good as the other professions, which were similarly boosted to account for Blacksmiths.
Yes, I know 4.2 sounds like 3.2 + 1, but it does not work that way at all. If you will recall, 3.2 was released as the third tier of raiding. Meanwhile, 4.2 is merely the second tier of raiding this expansion. We cannot rely on patch numbers anymore given Blizzard's new policy vis-a-vis "smaller, faster patches" (which I find unlikely will continue past 4.2, else we should have been hearing about 4.3 already, yes?), but it is safe to say that whatever patch will contain the third tier of raiding will also contain epic gems. But even more specific, epic gems will be in whatever patch includes updated profession bonuses. It has to, by design.
So until you start hearing about a stronger Mixology, Embossments, or Chimera's Eye cuts on some PTR, feel free to continue speculating on Pyrite and/or making bank on rare gem cuts.