The original Priceline kind of tried to do this. Not the change part, but you'd give them dates and a price and they'd give you the least-desirable possible seats on that date, presumably based on the airlines' needs (at least proxied by what the airlines were showing as the cheapest prices to Priceline).

The problem was that when I tinkered around with it, the price was never low enough to make me willing to play, suggesting the airlines didn't really need to do this. It couldn't have been too popular with travelers either. But I'd compute the value of status and miles, the value of my time in terms of the worst-possible option, discount that from the lowest non-Priceline fare, and take a shot. It always was rejected. I think a lot of Priceline's original business model was just people who didn't do any research or people who placed no value on earning miles or status.

In the U.S., starting in the mid-1990s (I think), the airlines were able to lobby the government under the ruse of "security" that they needed name matching. The reality is that it's simple revenue protection for them and another step in the erosion of individual rights vs. those of the corporations who own and operate the American government. Prior to the 90s, there was not a huge brokerage market like there is for concert tickets: that was not the airline's reasoning for requiring name matching.