Scalebound was a game that was anticipated by a whole lot of people and produced by one of the most prestigious names in game development - Platinum Games. Since the game's announcement years ago its development was rarely talked about, and it only ever got a couple of brief looks at E3 conferences. Just recently, the game was officially canceled altogether.
The cancellation came with something of a nuclear option on Microsoft's part, which removed mentions of the game from blogs and set all trailers and gameplay demonstrations to "private" on YouTube. Microsoft hasn't commented yet on why they've removed all of these trailers, or why the cancellation happened.
Chances are that Scalebound will remain a memory for Microsoft. Cancellations like this can happen for any number of reasons, but they're almost always final. Scalebound was looking like it was on the verge of entering "development hell" - that purgatory of eternal revision and financial disaster that did in games like Duke Nukem Forever. If that's the case, it might be better in the long run that Scalebound didn't see the light of day.