Airlines have enough bad press; it would surprise me if they raised the mileage requirements for reward redemption. I imagine that airlines want to keep people flying, so rather than play with mileage, I think they'd be better off to make rewards less available--something that I think could well have happened over the past five or so years. Another approach which seems to be gaining popularity is to keep reward levels the same, but introduce a new "more expensive" class that's easier to redeem. The airlines can still market the fact that they offer low mileage reward, but in reality one has to really splurge to make a mileage redemption!