It seems clear at this point in time that the Astros are headed to the American League. As has been oft-discussed, the inevitable consequence is interleague play throughout the year (see here for a brief overview of the potential ramifications). While the exact details haven't been hammered out, I have reason to be concerned from a Royals perspective.
It seems fairly likely that this will result in a net increase in interleague play (the above-mentioned link presents one possible model with 30 interleague games). The purist in me hates this, but that's neither here nor there. The DH issue is the real concern. Not having Billy Butler available other than in pinch hitting situations (which was more or less the case in away interleague play this year for the Royals) removes WAR and places the Royals at a competitive disadvantage.
Of course, this is just one possible model, and it only increases the number of games played in NL parks by six per season.. but six games can make quite a difference. It's nearly 4% of the season. As much as I know some of you hate the DH, it isn't going anywhere, and I honestly think the time has come to just institute it throughout the league to place every team on the same page.