Not wishing to get into a fight with you again - but you did.
You pointed out many of the problems with altimeters.
GPS has different problems. On balance it may well be altimeters remain the more reliable of the two BUT there is a trend to greater reliance on electronics if only because such systems are ultimately cheaper. I am quite certain if a sufficiently reliable and compatible alternative could be found manufacturers would be delighted to ditch encoders and altimeters for a self contained matchbox backed up by another self contained match box that did the lot. A loss of all electrical power is becoming an issue whether it be in a Cirrus or an A380. In a DA40 or a DA42 in fact you will find the engines stop - that may not be a good idea but it is illustrative of the way designs are evolving at the lighter end of the market.