The potential rain out will have an interesting effect on the series.
The conventional wisdom is that it will advantage the Yankees because it will allow them to pitch Tanaka in Game 4 instead of throwing a bullpen game. But, in reality, all it does is move some planned starts around without really changing how many times the best pitchers will throw in a 7-game series.
Below shows the probable shift in game days and off days.
Original: Game 1 - Game 2 - OFF - Game 3 - Game 4 - Game 5 - OFF - Game 6 - Game 7
Adjusted: Game 1 - Game 2 - OFF - Game 3 - OFF - Game 4 - Game 5 - Game 6 - Game 7
Basically, the Tanaka-Greinke matchup that was slated for Game 5 becomes the matchup for Game 4. Similarly, the Paxton-Verlander matchup moves from Game 6 to Game 5. For Game 6, however, it seems unlikely that either Severino or Cole would go on 3-days' rest, so that's going to be the Yankees bullpen against Houston's 4th pitcher, Urquidy - the matchup that had been slated for tomorrow night. Game 7 remains Severino vs. Cole.
Perhaps the most important effect is that the Yankees planned bullpen game would shift from the middle of 3 consecutive game days to the 3rd of 4 consecutive game days. If the Yankees have to use their bullpen a lot in Game 4 or Game 5, that could be an issue. It will be interesting to see if they might try and do something like start Sabathia in Game 6.
By the way, before anyone tries to point out that another rain out could lead to more interesting shuffles, no rain is forecast for Thursday or Friday in NYC, and Houston has a roof.