I got my sha touched gem last night. Cleared every boss on LFR and normal/heroic every week since available, got my last sigil of wisdom from HoF LFR before main raid did TES normal.
Can confirm that (for now at least) you are not eligible to loot more sigils after you have turned in the quest to Wrathion. You are left with a quest that says you have to wait for your faction's fleet to arrive in Pandaria ( says "[to be continued in 5.1...]").
*edit* now have over 20 sigils of power just sitting in my bags... not sure if I should keep them? I've heard rumours that apparently you can get another gem when you get a new sha touched weapon on heroic but I can't find any information on how.