No, they haven't. Also, the amount of difference between epic gems and rare gems is already known if you simply check Wowhead. And even if they had announced epic gems, your post doesn't contribute anything if it's devoid of a link or any actual discussion about them.
Blizzard has confirmed that they are adding epic gems in ulduar. I'm not posting from my comp atm so I don't have the link but its probably safe to assume an extra 5-6 spellpower per socket.