The easiest way to "speed up the game" would not require any changes to the rule book, wouldn't be noticed by the casual fan or most fans at the ballpark and it will never happen. You could shorten baseball by 8 minutes and thirty seconds per game at a minimum, not average, MINIMUM by shortening the half-inning break by thirty-seconds. These breaks are longer than they used to be, and longer than they need to be because of money. Greedy owners trying to get every cent from advertisers that they possibly can, and I think they are wrong. If you were to shorten the game by this 8 and a half minutes and maybe enforce some of the other rules (not automatically granting time between every pitch, not allowing pitchers to stall) could make the game more popular and drive ad prices up; therefore, making more money on fewer commercials. At the very least, they should let pitchers who are ready to pitch start before the media comes back from break.
Like I said: It's never going to happen, but it drives me nuts to hear baseball people complain about the length of games and never mention these crazy-long inning breaks.