NDBs have gone the way of the Dodo bird. There are only a handful left in the U.S. (along with the even rarer LOC BC) and I have a few bookmarked for clients who want their nonprecision approach to be an NDB or LOC BC. Our recurrent scenario uses KSNA runway 2L for the LOC BC and 9 out of 10 crews will choose the RNAV (GPS) approach over the LOC BC.
I haven’t kept up with GBAS (GLS) procedure futures since the equipment that I teach is not capable and there are only a handful of airports. Considering how expensive it is to install and maintain a Localizer and Glideslope equipment, I can see the cost savings with GBAS implementation. Just the airlines will fight it tooth and nail since the fleetwide upgrade to GLS equipment would be very expensive. They can also argue the same fuel savings and noise reduction benefits are available with RNAV to ILS procedures.
IMHO I can see one day in the future when ground-based navigation becomes almost nonexistent with SBAS and GBAS providing the lion’s share of navigation capability. Once the entire U.S. GPS constellation shifts to GPS 3 with its more interference-resistant signal and we get the ever-resistant General Aviation community to upgrade their fleet.