So my theory about why Versus was announced so early is because Square wanted another game to be developed on the very expensive ground up "Crystal Tools" engine. They didn't want to waste such tech on just one game. They probably wanted to ease the stock holders too that such an investment would help other projects too.
So they announced Versus. But after XIII-2 and Lightning Returns which actually did end up using the engine extensively and helping pay off the expense of this unique tech, they detached Versus. Couple that with Sony helping with the production for the PS4 you have a reason why the project moved on.
Pros of Versus moving to the PS4: Probably early release date, we won't have to wait for a couple of years.
Cons: I don't know how much of those Agnis graphics we will see with the project been based on PS3 for so long.
Pros of Versus staying on the PS3: 70+ instal base will enjoy the game.
Cons: PS4 Final Fantasy will take hell long to come out.







