Any A/P software which automatically descends the A/C to a lower alt, say FL140 or so, could be mighty exciting on the routes over Afghanistan or L888 over southern China!!!
IMHO what is needed is a very loud alarm which, as RYR posted, requires the oxy masks to be removed from their stowages. Remember that hypoxia is very subtle and, typically, sufferers are unaware of their predicament so it needs to be very simple and unable to be defeated.