Yes, but the signal GPS III uses cannot be read by current avionics or other devices. Which means when it is introduced new avionics are going to have to be released to support it. The manufacturers are based in the US.....they have WAAS......do you really think they will jump in first to release new avionics? That will lead us to the ADSB mandate issues all over again.
I think I can say I am agree-ance with you regarding a cost/benefit for SBAS as it relates to aviation. The numbers don't stack up, never did. But if we just happen to geta ccess to a WAAS signal due to other Government initiatives, shouldn't we jump on board?
If GA thought GPS III was a potential solution wouldn't they also be looking at that as well? Perhaps they are? As I mentioned previously GA are looking at many different future solutions. SBAS is just one.