Perhaps a software change to allow VNAV path indications to be displayed and crosschecked side by side with G/S indications (I'm thinking along the lines of Boeing's RNP/ANP display), or a FMC "G/S VNAV DISCREP" message to bolster charted altitude checks would be helpful in these situations. It's pretty scary to think that a single antenna failure would result in such indications, especially at unmonitored installations.
Cheers,
-Lee