Here is a short concept of Windows 9 in a Desktop use.
This screen below shows what the Lock Screen could look like with a Notification center.
On this 2nd screen, I imagined the new way to display windows : all rescalable, no frames anymore with a "at a glance" UI with clear button and icones. Appart form the windows, the UI is centered on a powerfull and universal search (aka Cortana) to allow basic and advanced user to reach and do what they want quicker.
The search could also execute some command such as : "write an email to bryan" > could open Outlook with a new email straight.
The universal Search agregates data from the apps, web, local files (including Onedrive).
A view with some of the trays expanded :
The bell icon is the notification center. It's foundable straight on the desktop for ease of access.
Any right click on an icon with the notifications expand more information and basic command (depending of the app).
The Multitask button can be activated by Win/Ctrl+Tab but also by clicking on the icon Multitask for an easier use.