Over the past week, MLB commissioner Rob Manfred and Cardinals GM John Mozeliak have alluded to growing support for designated hitters in the National League, which has resisted the rule since it was adopted by the American League in 1973. The commissioner has since backtracked, saying he doesn't see a unification coming anytime soon, and certainly not in 2017 when the next collective bargaining agreement will begin. There's a certain charm to the two leagues playing by slightly different rules, but the benefits the DH rule brings are hard to deny - it extends careers, boosts scoring, and eliminates rally-killing pitcher at bats and frustrating moves, like the eighth-hitter intentional walk. Some say it detracts from strategy, but do you watch games to see players play or managers manage? Seats at stadiums seem to be angled toward the field, not the dugouts.
Tradition and "purity of the game" arguments aside, it's easy to guess why some NL owners might oppose the addition of the DH. It would raise costs. NL teams would be trading the roster spot of a low-paid bench player or middle reliever for a spot usually filled by a veteran with a fairly hefty price tag. As pitcher salaries continue to rise, though, those owners might start to see the DH as a way of protecting their investments. A quarter of the twelve highest paid players in the game by AAV are NL pitchers Zack Greinke, Clayton Kershaw, Max Scherzer and Jon Lester. The idea of risking injuries to those kinds of investments - like the ones Scherzer and Adam Wainwright suffered in 2015 - doing something they're not even good at is just bad business.
The NL might not adopt the DH next year or the year after, but if they eventually do, how would that affect the Yankees? Most obviously, they and other American League clubs is they'd lose a decided advantage in inter-league play. The AL's record since inter-league began in 1997 is 2,565-2,299, a .527 winning percentage, which would produce between 85 and 86 wins in a 162-game season. We're not talking barely over .500 here. The AL has had the better record in interleague every year since 2004, and they've done it in 15 of the 19 seasons since its inception. The Yankees in particular have feasted on NL opponents since '97 with a 203-139, or .594, record.
When NL teams go to AL parks they're playing short-handed, slotting into their lineup someone who usually isn't good enough to start. Their opponent gets to counter with a player whose only job is to hit. When AL teams are on the road in inter-league, they do lose a bat, but it's rare that their DH can't fake it at a position for a few games at a time. Last year and for the next couple, the Yankees will avoid putting Alex Rodriguez in the field, but historically they haven't employed many DH-only's and that's only upped their edge over the NL.
Another way an NL DH would change things for the Yankees is in roster construction, or at least the cost of it. Players who DH primarily are usually met with somewhat lukewarm markets, since there are a limited number of teams who can use them. Nelson Cruz was coming off a 40-homer season in 2014, but he only got $14.25 million per year as a free agent. David Ortiz has been one of the bigger stars in the game since 2003, but he's never earned more than $16 million in a season. These guys aren't exactly cheap, but their prices would rise if there were 30 jobs available to them instead of 15. There could also be more competition for free agents who aren't DH's yet but are approaching that point. On the bright side, the Yankees, who generally employ a number of older, less rangy players, might have an easier time trading them when they need to clear a spot or some salary.
Ultimately the greatest change NL DH's might bring is in what exactly it means to be an NL or an AL club. If both leagues play under the same rules and if inter-league keeps expanding, as it has from 214 games at its '97 origin to 300 last year, then they'll start to look more like conferences, such as the NBA and NHL's East and West. That could lay the groundwork for geographic realignment, a concept that's been bandied about from time to time, but which has never gained any real traction. That idea would cut down on travel expenses and promote regional rivalries. In the long run, DH's in the NL could be the precursor the the Yankees and Red Sox sharing a division with the Mets and Phillies.