From Baseball Digest in January 1954:

Interleague in 1955? Well, apparently it was considered. Nate Dolin, the Cleveland Indians director of operations and AL schedule representative, wanted it to happen. He even got Walter O’Malley to agree with him. He proposed that the season would look like this:

• 158 game schedule (instead of 154)
• The 22 games-between-each-team-in-their-league balanced schedule would be cut to 18 games between each team in their league.
• Each club would have two two-game series with each team of the opposing league.

Of course, it never happened. But it’s interesting to note that, starting next year, interleague won’t only just exist but will be expanded: there will be at least one interleague game every day, since both leagues will have 15 teams.

But it could have happened… even earlier!