The packages from the "Modifier-only input switch" PPA work very well in case of Unity.
I've tried all the mentioned test cases and everything worked. The Ctrl + Shift L set as next source shortcut doesn't collide with Terminal shortcuts or Sublime Text 3 or LibreOffice. Also if I have Text Entry settings open and I issue the gsettings command in terminal the shortcut changes in those settings immediately (reflecting that change).
I don't have any other DE's except for Cairo Dock which has it's own session but I didn't check how it works in that.
The packages from the "Modifier-only input switch" PPA work very well in case of Unity.
I've tried all the mentioned test cases and everything worked. The Ctrl + Shift L set as next source shortcut doesn't collide with Terminal shortcuts or Sublime Text 3 or LibreOffice. Also if I have Text Entry settings open and I issue the gsettings command in terminal the shortcut changes in those settings immediately (reflecting that change).
I don't have any other DE's except for Cairo Dock which has it's own session but I didn't check how it works in that.