The GAs should be encouraged to make customers whole. That means if you scored a battlefield upgrade and all of a sudden a paid F customer shows up you collect your things and take the walk of shame to the back to steerage. It sucks but that's the right thing to do.
As far as pulling people up once the door closes I don't understand how there are any empty seats in the first place. With how DL gives away status like candy and FCM there should almost never be an empty F seat domestically.