While it's true that the ability to earn miles has increased dramatically in the past few years, in general the actual cost of travel has similarly decreased. Think about your FF life 2-5-10 years ago, how much effort did it take to earn an award ticket, and what would have been the monetary cost of that itinerary as a purchased ticket? Granted, it may have taken a lot longer to earn 20k-25k miles for a domestic US ticket, but they could be some pretty expensive tickets. NYC-LAX tickets were almost always $400-$500 or more, which means you were looking at a 2c/m redemption rate.

Fast forward to now, maybe that award is still 25k miles, but the $$ cost is MUCH less (just did a quick check for JFK-LAX fares, 10 lowest current fares range from $185 to $253 (plus taxes/fees)). While security costs and certainly fuel costs have increased over the last 2-10 years, because of all the cost-cutting, bankruptcy, etc, labor costs might be back at early-1990 levels.
10 years ago on United crosscountry flights, I remember getting a hot breakfast and a mid-flight snack (almost a boxed lunch), now most airlines offer little/no meal service, have to pay for liquor on int'l flights, etc. One can argue that what we get for an award ticket now isn't nearly as good as what you used to get. As pointed out, there's already been a significant devaluation of miles.

I think you might continue to see some 'periphery' tweaking of award levels, but I'd be surprised to see major changes to popular awards. I think as others have pointed out, being able to manipulate 'saver' award availability, and in many cases force people to use 2x miles to get a 'standard' award, will do more to limit their costs than simply increasing award levels.

Jeff