In the blog's comments, Felipe Morales linked this extension : https://extensions.gnome.org/extension/10/windownavigator/, and it's quite good. You can use alt+<Number> to select a window while in 'exploded view'.
[1]: https://extensions.gnome.org/extension/317/window-display/
The 'exploded' window view shows windows on current workspace so being able to select one from the keyboard means I can group the windows by task/project in different workspaces.
EDIT: I seem to be have been a bit confused before.
I think some functionality along these lines should be provided by the basic GS though.