This would be nice addition for SEV. A facility (ie. huge linear accelerator which goes through planet) which would allow to move a planet. For example, 1 sector in a turn. Of course, the cost of the facility would have to be at least equal to system gravity shield, so it would be not easy or effortless to do it.
Think, what kind of defence it would be to locate all planets in a system above the only warp point. 1000 WP:s to fire against attacking fleet before they get a shot
