…there will have to be an interleague game played every single day, with the 15-15 setup between leagues. But that also means that there can be a “super weekend” filled with nothing but interleague games and interstate rivalries. (Actually, such a weekend could be played with the current 14-16 setup, if the Phillies and Pirates play in the intraleague game, but MLB has never scheduled something like this to my knowledge.)
Here are the matchups that I would pick:
Mets vs Yankees
Dodgers vs Angels
Giants vs Athletics
Cubs vs White Sox
Cardinals vs Royals
Marlins vs Rays
Reds vs Indians
Nationals vs Orioles
All eight of these matchups are established regional rivalries.
Rangers vs Astros
Phillies vs Pirates
These two would be the only intraleague games played. The Rangers and Astros would be elevating their rivalry from an interleague one to an intradivisional one, so this would be only one of six series played between them. Similarly, the Phils and Bucs would be playing one series of two against each other, their rivalry having been diminished when the Pirates were placed in the NL Central.
Having all ten of these matchups all on the same day would provide for some very fun baseball.
There are, however, teams that do not have a regional rival and could potentially switch opponents every year.
Padres vs Mariners — These two teams already share a home-and-home series every year.
Brewers vs Twins — Formerly intradivision rivals, until the Brewers moved to the NL since MLB didn’t want to have daily interleague games — something that they’re actually going back on now that they’ve forced the Astros to move!
Braves vs Red Sox — The Braves franchise was originally based in Boston.
Diamondbacks vs Tigers
Rockies vs Blue Jays
MLB could really play up the AL vs NL split by having these games on the weekend before the All Star Break. With talk of reducing the intrastate rivalries to only one three-game series a year instead of two, this could be a new tradition in the runup to the All Star Game.