Do you really think that fans are just going to quit loving a team because it switched leagues? If they do, they're fair-weather at best. While the Astros do have history, and I know I would be quite angry were this happening to the Cubs, it's not the end of the world. As far as rivalries are concerned, they are walking into a ready-made one with the Rangers, one I would imagine is capable of holding far more local meaning and implications than anything they would experience in the NL Central. While it certainly is distasteful, even insinuating it is "market annihilation" is ridiculous. Meanwhile, while a 15/15 split isn't imperative for MLB, it is extremely productive as it will likely lead to an extra wild card slot per league, which in my opinion is a huge help for the game.