Now that Theatrhythm: CC has been attended to, SE might slip in a few words about it next week. But I don't think it would be a main presentation. They may be handling the marketing for it (thus far), but Nintendo should eventually help out in that department.
Remember, they have 4 booths planned for the event, and 2 "unnanounced game" presentations. I wouldn't jump the gun on predictions, being it that virtually anything is possible...well, you know, especially with Square Enix. You all know my hopes well.
I'd also like to bring into discussion the matter of the game's development. Although Tabata did declare that "100% will be given to development" for what was then Versus XIII, in 2011: it's highly debatable when DirectX 11-based development began, and when Versus XIII was overhauled into what we now know as FF XV.
By this time, the game has been in full production for around 3 years...but the game we saw in 2011 was radically different from what it has become. Practically a Kingdom Hearts clone, Versus XIII barely resembled the goals now aspired for by FF XV.
The development team did not officially decide to move development to eighth-gen consoles until 2012. It can be easily presumed that development was until then confined to PS3 development tools, and that DirectX 11 development did not begin until 2012.
Still, this puts FF XV right on track for a 2015 release. I do believe, however, that it will not be released until the second half of the year, allowing for yet another E3 showing.
We'll all find out next week, I suppose.
Source:
http://finalfantasy.wikia.com/wiki/Final_Fantasy_XV#Development