Double-Esc to close current window is huge. Looking forward to it.
Others here might come up with dangers of doing the above. Hope they will.
One possible issue: Suppose you have your Internet browser open with 20 tabs you are going to read. And you accidentally press Esc twice. Well....
On my keyboard, Ctrl-Esc is a handy combination, yes, so good candidate to do something with. Might, however, have to override a standard Windows action -- opening the menu, bottom-left corner. But I would prefer to override, as I never use the combo for that purpose.