GPS altitude : will not work below 3000 ft because the earth is not a perfect circle . Your C152 will find itself 1000ft below the ground in some places..
As said before WGS84 is an North American reference point made artificially to ensure positive altitude above its continent . Will not work in other parts of the world.
QFE. meters and Russians : This is not the cause of this incident . Tens of thousands of western aircraft fly every year since decades in this mixed environment without problems. I would say lack of proper training is . This is the common denominator of many incidents / accidents we see today. Add fatigue to that , plus fast airline expansion introducing new routes/ airports ,and not visiting them often and there you go.
Fixing the training issue would also far easier than changing Units of measurement on a global scale..
