I'm sure we'll see devaluations of some programs to come in line with others, e.g. AA might devalue post-bankruptcy. But remember the banks are actually paying for these miles, so in theory there should be graphs somewhere of what a single Delta mile has cost over time to financial institutions or middlemen like Cartera. Of course originally miles weren't being "sold" but certainly over the past 10 years there must be data like that (although I'm sure it's private).

I think some of the banks have begun to catch on to the churning game, we've seen some clamp down and the offers certainly aren't as lucrative now as last spring/summer. I'm sure there will continue to be great offers, but I remember in July/August there were posters who had racked up close to a million miles in just 2-3 months off of Chase/Amex's liberal policies of reconsideration and "bumping the bonus."

I do think the rate of devaluation is bound to decrease. What changes though are some of the rules surrounding redemption, to make redemptions cost less to the airlines. So even if quantity of miles for r/t air travel stays roughly the same from here on out for a decade, I'm sure we'll see more restrictions that curtail some of the amazing "aspirational awards" that those on flyertalk are great at weaseling out of the arcane rules the airlines have for redemptions. The recent BA program changes seem to be in line with this. For lots of normal fliers who don't carefully plan their redemptions they don't seem to be a big devaluation (indeed the YQ fees are the bigger of the two problems for most folks), but for the travel savvy on FT I expect further devaluations of the most lucrative front-cabin awards maximized with crazy routing.