I wrote a more in-depth explanation of this, but I thought it better to keep it simple and let the drawings do most of the talking. So here goes; an alternate design for Windows 8 multitasking which gets slotted into the transition mode (shown here) for the oh-so-satisfying app-closing gesture.

Edit: The Simple Explanation

Drop the app in the middle to get to other open apps.

Smaller thumbnails act the same as the big ones. Drag them to where you want them.

Transition screen:

1, 2 & 3 - Existing functionality of the screen

1) Drag down from top-center to enter mode

2) Continue to bottom to close current app

3) Release in side area to place in Snap Mode

4, 5, & 6 - Proposed additional functionality

4) Drag app across to secondary monitors (obvious)

5) Move app to Connected Devices

6) Release in center area to enter Multitask Mode

Animated Transition to Multitask Mode:

Upon release the large thumbnail scales and moves to 'Last App Used' position

Previously used/open apps populate the view entering in the same manner as Start Screen tiles (decelerated slide motion from the left)

Multitask mode:

1) Drag and release in side area to place in Snap Mode. After an app is placed in Snap Mode, Multitask Mode remains in main screen to allow selection of a second app or to continue with app management.

2) Tap thumbnail to open

3) Move app to Connected Device

4) Drag across to secondary monitors

5) 'Pick' thumbnails to allow multiple Close and Send to Connected Device operations. Eg. Send 3 selected apps to tablet.

6) Drag to bottom to close

7) Swipe to view additional pages of open apps (if applicable)

I feel this design makes better use of the currently underutilised transition screen and would behave how a user would expect it to. I think that this design would work better with a mouse than the current implementation whilst still being equally suitable for touch.

I recognise that this design doesn't fit the thumb control ergonomics of the Metro interface. As it stands, the existing design works really well for flipping through apps but even it breaks the thumb control ideals when it comes to setting multiple apps in snap. As this design expands functionality, there is an argument to include it as an additional means of navigation rather than an alternative.