I think they're going to be seeing which changes stay and go before changing others. I can see it being much different by the time 10 gets released in the middle of 2015. I know the OEMs keep pressuring MS to rush stuff for the holiday season at the end of the year, but it really doesn't work for MS. MS does their best work when they aren't being rushed.
MS would rather have a fully functioning os, rather than something half baked. The oems want it now, so they can ship machines preloaded with it, but MS would rather not face even more criticism for releasing something that is buggy.
All the new features in Windows 10 were supposed to be included in free windows 8.1 update, so it's only right to give windows 10 to windows 8 users free of charge, AND MAKE UPGRADE ISO FILES PUBLICLY AVAILABLE FOR THOSE WHO PREFER CLEAN INSTALLATION.
There had better be substantial changes if they don't want another market failure. From what I'm seeing in this preview, that's exactly where they are headed.
Start menu and Store apps in floating windows, yes. But the rest of the stuff... virtual desktops, notification center, Cortana, and all the stuff that has yet to come... these are features that weren't planned for a Windows 8.1 update. Therefore, most of Windows 10 features weren't supposed to be in this free update. By the way: I think the reason they dropped the Start menu from the August update is that it's just not ready yet. You can tell from the TP. I think they prefer to create a consistent UI (a.k.a. continuum) instead of putting a half-baked Start menu solution on Windows 8.1 that doesn't integrate well with its touch-first alignment. This has already been covered by things like Classic Shell. No, I think they put Windows 8.1 on maintainance mode in favor of Windows 10.