If they were to add in more stops, they would surely need an Express. If anywhere, probably when the joins. There are no modern 3T Peak-Direction projects that have happened recently, all of them have either been 2T or 4T. A 4T where the joins could enable the to run Express north, and the Local.
If they decided however to keep the stops that the concept map shows, a 3T would do the job. I am not sure if they are making a yard for the subway, but a third track could come in handy for not only this, but all times peak direction Express, being in the morning, the comes on the Express towards Midtown, and in the afternoon/evening, it goes out of Midtown. It will be the 4th 3T in manhattan, the , , and holding the other 3.