My Idea: STRG + Backspace to jump to the Taskmanager and STRG + Backspace at the Taskmanager to switch to the Application you have used before the last one.

So you should have the same like ALT+TAB. Only by clicking STRG+Backspace twice.

You can Vote here for Solution #4 at Brainstorm.
I posted this very late after the beginning. But I hope there could be more votes in the near future.