OK465,
the FAA has given up on GBAS
no tango dinero....
it is about as relevant as NextGen
Last news update was 2008....
Navigation Programs - GBAS - News
I have not heard of anyone looking at GBAS procedure designs in the US since Newark...and I work with Honeywell SmartPath...perhaps when Houston comes online...All of the work I know of has been only in certification.
The RNP to GBAS procedures I know of are in China..as well as a departure procedures.