Sony.

What do you mean "Why"?

I think that there will be no sequel, because the game will be a financial disappointment. 

Probably since that is the whole reason why they went to Microsoft with the first game, to retain the rights of this IP instead of giving them away like other companies asked for to give Insomniac financial support. But they could also have a contract where Microsoft has the right to assure a possible second or third game as exclusive if they pay them a certain amount or whatever...Nobody except for Microsoft and insomniac know all details of the contract (well, maybe some insiders)

It's probably going to be the Mass Effect scenario all over again, where the first one wasn't on the PS3, but the second one was!

it will come eventually due to low install base of X1 and people forget that fan base for insomniac is over at Playstation also whats the point of retaining an IP when you cant release it on other platform at best MS would have exclusive contract for first game and timed exclusive for second. But if successful this game will come out on PS4.

Although my theory is Insomniac R&C nexus team are working on a PS4 exclusive, it could be PS4 ratchet and clank to coincide with Ratchet movie coming out in 2015 or maybe a small R&C title like Quest for booty and new IP on which MS would have contractual obligation that for a year or so after SO release Insomniac should not reveal or discuss that they are working on a PS4 exclusive project

Doubt it. Microsoft can easily obtain the ip just like gears of war.

maybe

Simple, because they look really fun! Same with Titanfall, I would really enjoy them to play on the Playstation 4. Sadly, I can't afford both systems :/

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).