Don't change a thing. The 18-inning marathon was better than any Super Bowl, except that few of us were dressed for 45 degree weather. For dramatics, see the 1986 NL championship between the Mets and Astros, and then games 6 and 7 of that World Series. Everyone remembers Game 6, but the Red Sox had a lead in Game 7; the Mets-Astros final seemed like it would never end...Mets, visiting team, take a two-run lead in extra innings, and I got on a subway happy, got off to discover that the game was tied again.
You don't get that with a timed game.
I think the interesting stat is "Number of players used per game". See
http://www.baseball-reference.com/blog/archives/6927The line is fairly stable from 1920 - 1980, and very stable from 1940 - 1980...what I would call "classic baseball", the era of Feller, Spahn, Williams, DiMaggio, Mantle, Mays, Aaron and the rest. It angles upward from 1980, suggesting that managers now use more one-inning or even one-batter relief pitchers. The NL would use more pinch-hitters.
Anything that forces the pitcher or hitter to change would hurt the game.
On "number of pitches thrown", it's interesting. Pitchers were expected to throw more like 125 or 130 pitches per game. Paul Richards set a 100-pitch limit for his "baby" staff, and people ridiculed Milt Pappas and the rest of the Orioles staff. After the 9th inning of Game 2, I've come to think that a manager should leave a pitcher in until he begins to lose it. No "6-inning quality start", no 7th, 8th, 9th inning specialists. Each pitcher in each game is unique. Please, Matt W., don't script the pitching.