There are several problems with this:
The run OPTO 4 car R160s on weekends. R32s would increase labor costs.
There is not much demand for central Queens-Midtown service on weekends, and riders can just take the to the , , , or .
service on SAS is enough. No need for the , as riders have a cross platform transfer at 63rd, or they can transfer at Herald Sq.
A R32 breaking down on 6th will put it in gridlock, and if it does not break down in a station, then in the tunnel the AC will die quickly and the passengers will start to faint. Knowing MTA's terrible evacuation procedures, I wouldn't be surprised if passengers would die.
Also, with their declining HVAC units, the R32s will have to be put on outside lines. The is split if sent to 96th, and this is too risky for the cars. Best option they have is the Rock as any breakdowns there will not affect the line that much as they can easily be pushed by another train and relocated to Rockaway Pk Yard. Plus, Rockaway headways are so horrendous that nothing really would change.
Overall, this whole R32 and thing makes no sense. The should be fine on SAS, and if a extension is necessary, just send the to 96th with R160s.