User blog comment:Xhatefate/DxD Updates~/@comment-25136646-20140711164200/@comment-24502975-20140711174446

Well, I'd imagine all the Longinus possessors were young when they first unlocked their Sacred Gears. But yes, the Longinus of this generation are undergoing abnormal growth and the possessors of now will or already have surpassed the past possessors.

I'd say there are a few more before the climax, like maybe volume 22 or so. Which would be the appearance of 666. As for why he is working with Qlippoth... he isn't. 666 just desires destruction, and thus had to be sealed away. Qlippoth just wants to unseal him and teleport him to Great Red's location so they can fight.

Tiamat's name is derived from that myth, but I'm not sure how much it will have to do with the Tiamat in DxD's appearance or origins. Her being of Evil Dragon level would be interesting. Crom Cruach probably won't fight any Gods unless he joins Ise and co. after this arc, since next up is Shiva arc.

They will appear, there's no reason Ishibumi would leave them out. He also posted on his blog that there are 3 more members of Qlippoth to be revealed, so it would make sense for it to be them.