For now it seems PS4 will have better hardware than Xbox 720 or w/e M$oft will name it. But when will they be released is hard to guess because last year half of the analysts said we don't need next gen for the next 5 years and others said we need them now. Guess they could be out by 2015.
As for BF4, I doubt it has anything to do with next gen. Most likely scenario is DICE/EA being hungry for more money since Warfighter failed nicely. And if the rumors are correct about BF4 being even more COD friendly and just another modern warfare shooter, I'm not even going to bother getting it. Getting sick of modern day shooters. Bad Company 3 would be an exception here, but I really want to see BF2143.
Plus, why would they give Battlefield 4 Beta Access codes in Warfighter, if it was going to be on a completely separate console? That wouldn't really make any sense to me.
I read somewhere (Can't give you the source atm) that EA has announced both New BF and Fifa for the next-gen consoles. Plus I guess MS and Sony unveil their console even in the next E3.