In a GNSS RNAV system, we have to have a CDI with a localiser needle wired up to indicate distance off track. Many such instruments I have seen in this type of GPS approach application (E.g. King KNI 520) also have a redundant glideslope needle, sitting there doing nothing. Could the G/S be connected up, using the information from the altitude encoder and GPS distance information to provide a kind of non-precision glideslope? Surely, what we need is some sort of secondary check to make sure we are not getting too low at the wrong waypoint. At the moment, if we do mistake an intermediate waypont for a later one, there is no secondary check to tell us we are getting too low, unless maybe we have a switched on, qualified co-pilot of course.