I'd throw next gen out the window, a nice system, but subject to far too many errors, and it has NO backup.... which means that at some point somebody will notice that and THEN decide we ALSO need to keep our nationwide traditional radar systems up and running as backups, and then we LOSE all the long term cost savings this idea brings... it also is a bad idea in terms of national security... NextGen would not show a cessna slipping across the border at 2000 feet from Canada with no GPS driven ADS-B system, and there would be no primary target only displayed.