I think an option to remove ownership of a province would be great. It'd allow people to seperate portions of the map, or set the focus of a game around a specific area.
Example: Remove ownership of every nation outside of Asia. This way, the only active nations are asian ones, which cannot interact or grow outside of Asia.
If people want to remove wasteland, they could simply transfer it to an active nation and/or release nations which have claims there(via TAG command).