One thing you gotta say about S.E, they sure do know how to make a damned good trailer. Not seen that one before and when the hyped up battle music kicked in I got a shiver down my spine XD

Also notice how during it there's a guy that looks like he's walking along a cliff-edge in Thanalan? Can't say I've seen that area in Thanalan so far.

Titan will probably just be included in a later patch, S.E needs to build up a player-base for the game first so it'd make sense to go for a boss such as Ifrit, that players are more familier with, in order to draw in the crowd. The next one may be Shiva, Titan, Odin or even Bahamut. (Though I can't see them using Bahamut this early in the game, he'd probably be way in the future when the game has built up a lot, so the battle against him can feel more epic)