On some systems, anyway. According to sources familiar with Microsoft’s plans, traditional desktop and laptop systems will revert to the “classic” interface after the update. It’s a logical move. The touch-first Metro interface has never been a great fit where a keyboard and mouse (or trackpad) are the input device of choice, despite Microsoft’s work to improve things. Even with greatly improved hotkeys and mouse controls in Winodws 8.1, the Metro interface still didn’t win over many non-touch users.
On phones, tablets, and hybrid devices, however, Metro will still be front and center. Mary Jo Foley’s sources tell her that on 2-in-1s like Microsoft’s own Surface Pro and the Asus Transformer Book, Windows 9 will also recognize when input peripherals are attached and respond accordingly. Clip on the Type Cover, and your Surface will default to the Desktop and Start Menu when you wake it up.
What’s not clear is what will happen to all-in-ones and laptops that feature a touchscreen. It ultimately won’t make a whole lot of difference what Microsoft decides. If they’re putting these UI changes in place, it’s all but guaranteed that you’ll be able to specify which one you want to roll with. They already gave us the option to bypass Metro on startup, after all. There’s no reason to think that they’re going to lock us in to a specific UI simply because we’re using a device with a touchscreen.