Read tanking guides, i know that Tk:s get the ability to have 3 cubics, but can they summon 3 of them all alone and have all 3 of them up ? (tanking guide talked about this maybe implemented in C4 with summoners).
As far as I can tell from interlude patch notes, TKs are getting their 3rd cubic in Interlude. It's the "attack cubic" and casts hate on mobs as far as I can understand. In the meantime they can have two out at once and if a summoner is in party they can get the 3rd via mass summon cubic that Elemental Summoners, Warlocks, and Phantom Summoners get.