Bill James answers (lots of) questions at Freakonomics.
He made an interesting proposal:

My pet project is a rule to limit pitching changes in the late innings. My rule, specifically, would be this:
1) Each team is entitled to one unrestricted pitching change per game.
2) With the exception of that one unrestricted change, no pitcher may be removed from the game in mid-inning unless he has been charged with allowing a run in that inning. With an exception for injuries, of course.

When you propose a rules change like that, people say, "Oh, you’re changing the way the game has always been." That’s nonsense. In 1970 major league teams used 1.75 relievers per game. In 1990 they used 2.02 relievers per game, and in 2007 they used 2.97 per game — and the rate of increase in this area is still accelerating.

I'm generally wary of any rules changes, but this would be a way of speeding up games a little and would merely be combating a very recent innovation in the game that is generally annoying. I think it's probably a little too restrictive, but some limitation on reliever substitution would probably benefit the game, even something as simple as requiring that a reliever face at least 2 batters (unless the inning ends).