Claiming that Dust 514 is a cross platform game is only half true.
While EVE Online players on PC will be able to interact with Dust 514 players on PS3 they will be playing entirely different games, the 'cross platform' comes from events in one having an impact on the world in the other.
It's not the same as Portal 2 by any stretch, which only succeeded because it was a cooperative game and not competitive. The last time that was tried was, I believe, Shadowrun which crashed and burned because it was a FPS and people on consoles couldn't keep up with PC players who, through M&K controls, had an inherent advantage and higher skill ceiling.
Sony is also unlikely to truly open their systems as that would reduce the level of control they have over their hardware, something they have, for better or worse, vehemently defended over the years.