It's certainly very plausible we will see Gears on the PS4 (and perhaps PS3, depending on the time frame during which the game goes multiplat), however, Epic would need to consider a few factors before going forward with it.
For starters, The game would obviously sell considerably less on a PlayStation console since the series and it's following have always lived by the Xbox. Epic would need to consider whether losing the likely large amount of money MS provide Epic for marketing etc would be recuperate by the PS's release.
Looking at the numbers for how it went with Mass Effect (though of course ME was never a true xbox series with all games appearing on the PC) I'd say in all likeliness, it would be well worth Epic's time.








