Yet another infuriating problem with updating to the GNOME-based desktop is that it lost my keyboard shortcut settings.
Worse yet, it's evidently impossible to assign custom commands to certain key combinations. Namely, I used to use Super+Alt to launch the overview in prior Ubuntu releases (at least I think that's what it was called; the system pop-up where you can launch and find things. I tire of trying to memorize the flavor-of-the-week permutation of generic words like "activity", "overview", "home", "launch" etc that projects cycle through with arbitrary distinctions between).
In any case, Super was the default binding for this in the Unity environment. GNOME splits it into two different options; one with the app list, one with the search box. Whatever. But I needed to rebind the key combo to "Super-Alt" before the upgrade, because I have a specific app I use that captures raw Super key usage. Super is next to Alt, so this is the best compromise.
In GNOME Shell, however, you can't use "Super+Alt" for anything. Super alone, fine. Super plus a character key, fine. Super plus a modifier, up yours. It doesn't even report a problem, it just doesn't capture the combination in the "Enter the new shortcut" dialog box.
I know enough to know there's surely a way to manually configure this through flat file editing, but man is it annoying to have dig that deep in the mud. There is literally no advantage to disallowing specific key combinations as shortcuts. And I guarantee you that if I filed an issue on this, the response would be "well just use a different combination then". In other words, you're using your house wrong.