Users running Threshold on a desktop/laptop will get a SKU, or version, that puts the Windows Desktop (for running Win32/legacy apps) front and center. Two-in-one devices, like the Lenovo Yoga or Surface Pro, will support switching between the Metro-Style mode and the Windowed mode, based on whether or not keyboards are connected or disconnected.
The combined Phone/Tablet SKU of Threshold won't have a Desktop environment at all, but still will support apps running side by side, my sources are reconfirming. This "Threshold Mobile" SKU will work on ARM-based Windows Phones (not just Lumias), ARM-based Windows tablets and, I believe, Intel-Atom-based tablets.
There was also this great post on Reddit a few months back from a Microsoft UX Designer. Basically he says Microsoft was tired of not being able to properly cater to both casual and power users. So the casual user being their larger demographic, they made the default experience in Windows 8 catered to them. If the default was still the old desktop interface, causal users would never switch to the more casual-catered experience. Moving forward, Microsoft then implemented an option to boot to desktop directly. And soon we'll see the next major Windows 8 update (8.2?) re-introduce a proper Start Menu.
Edited by WhiteZero, 01 July 2014 - 08:48 AM.