I agree they could have had this open weeks (actually, months) ago, but I don't they are delaying because they want to steal Potter's thunder -- Potter is going to take all the wind out of the sails for any marketing Disney is able to pull off with this nice little addition. Potter is an entirely new land with two epic attractions. Mine train is going to open first and then, a few weeks later at this pace, Potter is going to open and draw all the buzz. Disney isn't doing themselves any favors here, unless they actually are starting to drink their own kool-aid and think this attraction has any chance of competing, from a publicity standpoint, with the buzz potter is about the generate. Anyone remember this:
http://www./wp-content/uploads/2010/06/54408252.jpg
Prepare for round 2 -- bigger and better. As much as I think the mine train is a great addition, it is not going to generate the kind of fervor Potter is about to just a few short weeks after the mine train opens.