Here's my cockamamie idea for radical realignment: base it on market size, geography, and common or uncommon sense.
Basic premise: Six divisions of 5 teams each.
Interleague play: Two options. One is to do away with American/National, and just have MLB, so it's all interdivisional play. Interleague play becomes a non-issue. The other option is to split my divisions into AL and NL, and in that case, interleague play every day. Deal with it.
DH: Either have it or don't, but discuss it in some other thread. I'm not a purist, but wouldn't care if there was no DH. But I'd rather have it one way or the other, not both like we do now.
Scheduling: Unbalanced, NFL-style. Play more games intra-division, and a set number of games against other divisions. More on that at the bottom.
Why it'll never fly: MLB doesn't want a division like my AL East. They don't want the possibility of one team making the playoffs from that division, they want all of them to make it. In fact, they want my AL East and AL West teams to be the playoff teams every year. My system is much too fair. On the other hand, the Yankees and Mets would play 16 times a year or so, instead of six, so maybe they'd go for that tradeoff.
The hardest part was the Western divisions. To make all division have the same number of teams, the Texas teams are "western". So let's start there.
NL West, or MLB Mountain Westish
Oakland and Seattle switch leagues if it's AL/NL. They don't have the tradition to complain. Oakland should just move to Sacramento or something, but I don't think that changes anything here. There are some sub-major but still large markets in northern California, but I don't know if they favor SF or Oakland or LA or who, so I'm open to shuffling these two decks.
AL West or MLB West or Big Money New Money Westernish
Houston, SF, and LAD switch leagues. Houston doesn't have the tradition to complain, and SF and LAD are historical carpetbaggers anyway. They get what they deserve.
AL East or MLB Big City Fat Cat Rich Guys or Something
I don't see the Mets having a huge connection with the NL. Philly yes, but something's got to give. One thing about the 15-team division idea is that the Yankees and Boston will always make the playoffs (that's why MLB is floating the idea). My way, the rich guys can fight for one title and a wildcard.
NL East or MLB Misfit Second Cityish
Splitting Chicago makes the market sizes match up well, even if the Cubs are more popular there. Toronto might fit better in the Big City Division, but it acts more like it belongs here.
AL Central or MLB Centralish
STL is an NL Team but preserving league ties really isn't important to me. It's a new generation.
NL Central or MLB Runts
Switching MIL and STL wouldn't bother me, considering MIL's sweetheart parking revenue situation. That would fix the NL purist objections, and in almost any arrangement these last two divisions should be competitive among all ten teams.
Overall, if it's AL/NL, the bigger markets are heavily on the AL side. I'm not sure if that's good or bad. The point was grouping market size, so it would still be the big markets duking it out in one league too.
Playoffs: If AL/NL, three division winners, one wild card. If MLB, six division winners, next two best records (so it is possible to have three teams from one division make the playoffs). Seed the playoff teams by record. I think MLB really wants 10 playoff teams, but the issues they face with that are pretty much the same under any format. That is, you can't do it without a playoff bye for two teams.
Schedule could be concocted a number of ways. Similar to the NFL, you could play your own division a bunch, and three other divisions in a given year. The following year, you'd play the two divisions you didn't play in the previous year, plus one that you did, and just keep rotation the three other divisions you play.
Or you could play every division, 4 games each, rotating home and away each year. That way, every team in baseball would come to your town once every two years.
Or... any number of other ways.