Talk of expanding the playoffs in the immediate future seems to have died down. That seems strange, given the exceedingly boring nature of the races this year.
In the AL, the Yanks and Sox are in. No drama there. Detroit has a pretty solid hold on the weak Central. The Angels still have an outside shot at the West, but it's not likely. The Rays are 7.5 games out of the Wild Card, so nothin' doin' there, either.
This makes the AL Wild Card pointless. Neither East team has much incentive to try to beat the other. Home field advantage is nice, but resting your starters and setting up your rotation is better. Not even ESPN can cook up something interesting to say about that race.
Things aren't much better in the NL. The Phillies have it wrapped up, of course, as do the Brewers. The Cards and Giants are about 9 games out of the Wild Card, so you can hand that to the Braves. Unless the Gigantes somehow discover the secret to scoring runs (hint: get some hits first), the D-Backs will take the West.
So, here it is September 1st, and all the races are basically wrapped up.
Now, pretend with me that there was a second wild card in each league, with a one-game playoff. In the NL, the Cards and Giants would be feverishly trying to squeeze ahead of each other, currently separated by half a game. If the Cards win, you move the last game (Wed Sep 28th vs. Houston) up to a day game. Thursday the 29th, Cards play the Braves in a winner-take-all. You add one solid playoff race (Giants/Cards) and make the Braves sweat out the season, trying to catch Philly to avoid the 1-gamer.
In the AL, Tampa Bay and the Angels are separated by only 1.5 games. So add another race there. And now, down the stretch, you have the Titanic Struggle of All Titanic Struggles, where the Yanks and Sox claw and scratch for the all-important division title. Nobody wants to face either the Rays or Angels in a 1-game series.
So, instead of exactly zero interesting races, you'd have 3 interesting races, with one of them dominating all MLB sports coverage 24/7. The beauty of the second wild-card is that it actually makes winning the division more important, not less.
More revenue, more excitement, more importance on winning all season long. What's not to like?