The only line serving Midtown East is the Lexington Ave (4,5,6). The next 20 years will prove to be more crucial in building all the phases of 2nd Ave Subway. With towers like 1 Vanderbilt, and dozens of other thousand footers popping up and bring more office workers into an already congested area, there is a need now more than ever for not just a 2nd Ave Subway, but additional modes of transport to alleviate the Lexington Avenue Line, and the area in general.
Many of the workers will be coming from Brooklyn, Upper East Side, and Queens. For two of those three locales, the 4,5,6 are needed to get to Grand Central - 42nd. These developments will further push the need to attain funds to finally build phases 2, 3, and 4 of 2nd Ave Subway.
Two lines to get to 1 Vanderbilt and Grand Central currently look like this.
7 line
Lexington Line