I don´t know if it is technically possible.

the idea is to use the overlay mode to manage windows i.e to perform actions like

1) closing windows (single or grouped windows). This could be done using a right-click menu or dragging the windows to some corner... 
2) fusion "same-application-windows", eg drag and drop one nautilus windows with two tabs onto another nautilus windows with 1 tab create a single window with 3 tabs (same behavior with firefox gedit, the terminal etc)
3) order windows. Drag and drop windows while holding "some-key" pressed allows to organize windows onto a grid. Once you left overlay mode the ordered windows remain at their position onto the grid, eg if you are running five applications you enter overlay mode and 5 different windows are showed you put two of them onto the grid (Drag and drop + "some-key"), you left overlay mode and the you get the two windows covering the screen and each windows occupied half the screen (it would be nice if gnome-shell allows to put onto the grid two, tree or four windows, more than four could be nonsense...)
4) other actions?


Thanks in advance.