I think that what twistedenginestarter meant to say is ... "NASA or FAA have analysed this in great depth and if I remember correctly they think several new things will have to be added to permit sole enroute use." Primary use is already available in the USA, Australia and, yes, even in little ol' Papua New Guinea.
Nobody's game to bite the bullet on SOLE use, for reasons of reliability, as already stated here. The problem faced by the US FAA is that they've pinned their finances and reputations on WAAS. With this in place, sole use becomes feasible. Sadly for them, the work on WAAS hasn't been going well and, if memory serves me correctly, the US Vice President (perhaps the previous one) stated some time ago that it was highly unlikely that SOLE use would ever be possible.
Even so, the technology is pretty good the way it is. The experience in PNG, aside from a few cowboys who didn't live long enough to appreciate the system's limitations, is good. We get excellent satellite coverage here, being so close to the equator, so we're very happy with the level of operational approval that exists right now.
Of course, we also don't get the sort of interference that has happened, for example, in Italy. Very few FM radio stations and very few radio-controlled taxis and buses. I know that it's horses for courses, but as far as we're concerned, this horse is a real winner!