Well it sounds like there aren't many options available.
Airservicess' website says that the GBAS is the ILS replacement, yet it doesn't seem to be catching on anywhere. People are building replacement ILS's not GBAS systems.
After reading this it sounds like yet another aviation infrastructure project that will meander on forever with no decisions being made because it's all to hard.
Guess the RNP is the best of a bad choice.