Let me just start off with the fact that I think crazy-long extra inning games are fun. Not only is it free baseball, but there's a greater chance that weird and/or exciting stuff happens.

I am also aware that the MLB has taken measures recently to try and speed of the pace of play. I oppose most of these moves, as the lack of a clock in baseball is part of what makes it baseball. So, if the MLB really wants to make extra inning games shorter, I have a few suggestions.

1. Have ties. All games are nine innings, no exceptions.
2. Let's just take these problems and push them somewhere else.
3. Start each inning after the 9th with the bases loaded. The MLB has already proposed something similar, suggesting each extra inning begins with a runner on 2nd base. However, my idea is better because bases loaded situations are exciting, attracting more fans, generate more runs, and end the games sooner.
4. Each extra inning, the fielding team can only field a pitcher (duh), a catcher (duh), two infielders, and one outfielder. This, like the suggestion above, will end games sooner and generate more offense, which, as we all know, is the only exciting part of baseball.

Like I said, free baseball is one of the most amazingest things in this world, and there are no problems with it. However, knowing the MLB and them wanting to make shorter games with more offense (which isn't how baseball works), these definitely may be viable solutions.