AF/KLM (soon to be renamed America France Airlines) have already started down the slippery slope of XP being based on spend/fare type. Toss in BoB and the Superlight/Basic Fares. Down the road, your eligibility for an upgrade (and price) will also depend on your fare type; Superlight fares will not be eligible for OLCI upgrades, whereas Full Flex will have highest chance/lower cost.

It won't happen overnight, or even this year, but in the next 3-5 years ? Probably.