I'd say the point of a thread like this is to dream big. While those ideas might not be implemented, if we don't dream big than the developers may not know what we MOST want. Even if those are impossible creations, they can use that to guide the mode's creation.
I like the procedural generation model Ayvah has put forward. It's still a far reach, surely, but if GM mode is to be accessible AND creative, custom and easy map creation would be a huge plus. I'd rather other resources take priority, surely, but if it was something they had time for... great.
