lol...i didnt even think about this until now...Makes sense to me as he wants tons of souls and all...However, super bot might not be telling us something...What if there is more than one boss in the game that we dont know about.
IThat would be really weird, but SSB has a giant glove, so.. lol. Honestly, I think it's Kevin Butler!
EDIT: Then again, what about MGS? MGS has been PS exclusive mostly, up until the HD collections. Maybe it could be Liquid? Metal Gear? It doesn't sound likely at all, but I think fighting Liquid on MEtal Gear at the end would be awesome.
Heres my guess
It wont be a well established playstation character because thats would make people question why they arent playable.
I would imagine it wont be a specific end-game boss from any game.
It will most likely be similar to the masterhand from Smash bros.
With those things in mind you are looking at either a kind of creator boss or an embodyment of playstation.
A giant hand.
A playstation logo
A combination of many playstation final bosses.
God of the playstation universe xD