I know the USA is a totally insignificant part of the world's aviation scene, but before deriding this proposal as [various shades of] nearly impossible, has anybody asked how it works over there?
I recall being in a UK CAA presentation on GPS approaches, c. 2005, where the presenter (now a very high ranking figure in FCL) said that the CAA "found" that the FAA never analysed the reliability of GPS... So the CAA paid a bunch of consultants a load of £££ to do a GPS realibility study.