AlphaC,
On multiple occasions I have referred to the Minister's statement re. SBAS/WAAS being a "revolution" for aviation, all my comments are directed at that.
As for terrestrial use, all the claims for use of SBAS/WAAS are as true now as they were almost 20 years ago.
The big difference is that GPS III is now fact, not something in the near future, while SBAS/WAAS is, as it always was, a solution to the errors of the single channel civil GPS.
And I would suggest that, with what we already have, better than 3-5cm is available now, but, of course, we are getting to the situation of: How do you measure the order of accuracy??
Without going into the mathematics applicable, funnily enough, we are back to a "most probable position" from multiple readings, just like when I first did astro-nav, but now the circle of uncertainty is just a tad smaller.
Tootle pip!!