I doubt Tizen will take off. Samsung's software prowess is nowhere near to companies making and capable of making world class/sophisticated OS(or mobile OS). There is a lot of things that goes against Samsung which is in the company's DNA (culturally embedded it) and those are the things that hinder innovation and cutting edge research(esp. from s/w research perspective). (Probably the same things actually help them do great in the numbers game and on factory floor)

And even if it does. Samsung is the one vendor that actually sells Android phones - those millions of phones and I am sure Google gets a cut from it, not to mention ads and other ways of monetization. So, it is unlikely Google is denying them early code access. Other OEMs have failed on one more front - providing upgrades and this is where Samsung beats them all (except Nexus line; last 2 Nexus were from Samsung BTW). HTC makes good phones(better than Samsung IMHO, at least some models) but their users are doomed on upgrades. LG is not even worth mentioning. We have their phones in test lab and almost they all suck. We've yet to see where Moto goes and what it does. I guess Google will try to pull an Apple with Moto(though it's just a guess, I've no solid backing for this argument). Sony just keeps trying to make their devices all the pretties and they end up screwing the overall design and their s/w support is even worse than LG.

Tizen is not fragmenting Android. I also had doubts about it and talked to the guys working in that team and they explained it doesn't. They also said that Tizen Android app experience is nowhere going to be near the native Android experience.