From what I understand, I'm under the impression that Insomniac Games retains the rights to Sunset Overdrive, so first of all, it will be up to Insomniac on whether or not they decide to bring a potential sequel to the PS4. With that in mind, I would imagine that the exclusivity of Sunset Overdrive depends on the success of the game, the success and market share of the home consoles, and finally, how much each console company is willing to pay.
For example, let's say that Sunset Overdrive does well, but maybe not enough to where Microsoft is willing to remain partnered for the title (i.e., they aren't as interested in paying for exclusivity); in this situation, I could see Insomniac deciding to take the franchise multiplatform for their next game. Similarly, let's say that Sony continues to lead home console market share with the PS4 a year or so from now, which may make Insomniac feel like they can't ignore that user base, regardless of how much Microsoft is willing to pay/do for exclusivity (especially when you consider that many of Insomniac's fans may still be a part of the PS4 user base); in this situation again I could see SO eventually going multiplatform.
Obviously, the short answer is that it could happen, but we'll ultimately have to wait and see. At this point, I wouldn't wait for Sunset Overdrive to appear on other platforms (i.e., if you want to play it, it might be a title that may convince you to get an Xbox One), but at the same time, I wouldn't be the type of person to say that it will never come out for other platforms (because of the possibility of feasting on crow).







