I doubt how popular the will be compared to (or SAS ). People like the SAS because it brings upper east side residents to the west side much easier than before.
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On the SAS .... One of the options would be swapping the northern terminals for and , where runs on Broadway express, and use 63st to the Queens with same extra s going to SAS. goes to Astoria. This way the and are basically running independently without sharing tracks with anyone else ( all use 60st now, mixing of broadway express, broadway local, and queens blvd local). That would make the Broadway line to be a bit more reliable.
Down side.....no yards on the both sides of , and Astoria loses Broadway express service.