Split Windows would require fundamental changes in the OS, and certainly even in at least some of the apps. So if that feature is not in the early builds, I take any bet it won't be in the final one either. That's nothing Microsoft could add last minute. If it were in the works already, don't you guys think information about it would have been leaked? Well, nothing so far. And with an approximate release date of late summer or fall, there's not that much time left to implement a heavy weight feature like that. Interactive live tiles require fundamental changes too, but in this case at least we know Microsoft had already been working on it, so it could be available at some point of the Windows Insider program.