ErmengardeStopSniveling said: "FWIW, I thought OP's observation was interesting and something I hadn't thought about till it was posted. The only issue is that it was posed as a question instead of as a fun fact about where the shows were opening.
C'est la vie."
I thought your original analysis was spot-on. Essentially I was thinking what you wrote, but too lazy to do the work to support your comments.
Ironically, whether or not they typically prefer new shows to revivals, I would bet that the Shuberts would have preferred this season to get Cabaret and Merrily into a Shubert house over a number (most? all?) of the new musicals that are booked into Shubert houses. I would imagine that, by the end of the season, those two shows will have opened with the biggest advances and probably been the two biggest hits of the season. I have not read anything about Cabaret's sales to date, so it may not be selling as well as I assume, given its prices and the fact that Eddie Redmayne's star is a little less bright than it was a few years ago.