Instead of telling Gazans to all go south, why don't they set up some safe zones in Northern areas controlled by the IDF? They could bring in full supplies of everything, let people leave Gaza, and/or allow them to go to the west bank if they choose.
It's a pretty good idea. But they're probably worried about terrorists squeezing through. Egypt's already had to halt some of the refugee routes because they caught a few terrorists sneaking through.