First of all, I have noted for some months that even though I have Colemak
selected as my default, sometimes on boot I get thrown into Qwerty. That's a
minor issue for some other time. I attempted to install the Greek polytonic
keyboard layout via System Settings, and never got it to work with input
switching via the Super+Space shortcut or at all for that matter. I even
installed Greek language support, but that apparently did nothing. Best of
all, I'm left with no less than 19 selection options when I hit Super+Space,
but NONE of them are Greek Polytonic.(Just repetitions of English US)
Furthermore, the selection screen is chopped off to the right so the whole
thing is a big mess. I will post if I find a solution, but for now, Ubuntu
has us beat on this one.