Finally decided to draw the exact layout of north of 57th (which I've been mentioning/describing for years), to show the easiest solution. It's actually constructed as a "Flying junction", and the 60th St. tracks don;t become the local tracks, but rather "wye" into both the local and express trackways, from inbetween them. Only the local trackways were never used. The orginal four track line was built to veer west and continue uptown, and the 63rd St. connection simply cut across the ROW, to head east.
So right away, the north trackway (A2) leads right into the north 63rd St. track (G2), but a concrete room has been constructed on the trackbed. That can easily be removed, as it is simply block construction.
It's southbound, where the local A1 trackway veers away from G1, and then the columns between A1-3-4, etc. are present, that more work would have to be done (to remove the columns, the load bearing of the tunnel roof will have to be redistributed with all new horizontal beams). This will be the main problem.
At one point, before it was mandated that the full SAS would have to be planned (and not just the uptown "stubway") in order to receive the funding, they were talking about reconfiguring the whole Prince-Canal st. junction, to allow the SAS and express to feed directly to the downtown tracks, and the local tracks would then lead across the bridge.
This would require a tremendous amount of construction, including most likely, property acquisition (you would have to make the tunnel wider to have the trackways make the swap, and there isn't much space on Broadway).
But just making this relatively simple modification north of 57th, then they could have a local connect to 63rd, and the express switch over to 60th, without crossing over each other. (good for unplanned reroutes and G.O's as well).
Even if they did just the northbound, that would help a lot. with the reroutes. They really should look into doing this now, because when the is carrying a huge chunk of the riders next year, this cutting it at Essex or Chambers everytime something goes wrong anywhere on the IND (especially Queens, of course), isn't going to cut it.
If in Queens (or the rerouted via 53rd), it will be better to cut the back to 57th, and then let all 's run to 96th. With the northbound connection, the northbound express could be the "pocket" for the , and yet some could still run around this on the local, and run through, so that there is still access from Bway above 34th, to SAS, and it would alleviate congestion with the single pocket filled; (and 's could be run through 63rd if needed) and the southbound track would still be open for the through service in the reverse direction.