The most I can see happening in terms of minimum batters faced by a reliever would be that a pitcher who comes into an inning clean must face at least three batters, excepting injuries. Guys brought in during an inning, or with men on base, may well yet be allowed to face a single batter.
Similarly, they could invalidate the "starting reliever" concept by mandating, again except for cases of injury, that a starter must face the opposing team's lineup twice through before he can be pulled. That would limit the games where a starter walks two in a row in the 2nd inning, gets pulled by a paranoid manager, and then we see every reliever the team has shuttled into the game over the following seven innings. That is the scenario guaranteed to create the longest, most boring games.
I also betcha that if TV commercial breaks were banned during pitching changes, they could be accomplished in 20% less time.
So, there's a lot of meat they could get into during these discussions.
-Doug