It is confirmed by Tabata that the creature on the chair is in fact
Ifrit. My initial reception of seeing him back when we got that tease where he looked all thin and mangled is what put me off entirely for the most part. Once we saw him in Chapter 0 however, it looked a lot more like Ifrit as
@DrBretto pointed out with the FFVII design just maybe a bit leaner.
The leaks before mentioned Ifrit, so this is supporting this theory, however, again, it can very well be constructed by seeing this material before hand and coming up with some ideas. Or, it very well may be that they do have insiders within the company.
As the leakers have mentioned though, they've been fed some false information though, so we'll have to see what turns out to be true or not. This is probably the last I'll speak of these leaks though, as I feel it's best to focus on the game's release. Once the game comes out, we can have plenty of discussion on what was real and what wasn't.
For the purposes of this thread though, Ifrit is in fact the creature on the throne, also, it was confirmed that this isn't the final boss of the game. Personally, I expect to fight Bahamut as one of the final Astrals in the game, as Bahamut is usually the most powerful of the Summons. We will see though!
I wanted to be the one to post this given how strongly I was against this being Ifrit to show that I am not at all resistant from being proven wrong.