The preview-tabs is indeed a must-have, good thinking!
I like the idea of invoking commands to Visual Studio, as you show in the search box. However, allthough it is definitely handy when missing a command-window, it just feels wrong to use a searchbox for commands (instead of "search").
Having a Powershell enabled command-window available all-the time would in my opinion have been a better choice.
I can also think of extensibility options for such a command-window: see the NuGet Console window, which in fact is Powershell enabled. Why would anyone need to "invent" such a command window? Why not enable people to put their efforts in the actual commands they want to expose?
It would be great if we could just type "New-Project" or "Attach-Process" in such window, instead of in a searchbox. No need for fancy UI, intellisense could work just as well in a commandline window. Using the searchbox, people need to know the commands anyway.