Platforms are 170ft. The southbound side has the space to extend the platform (to 300 or back to 480, not sure about 600, as there are overpass supports past 480, so if they went past there, it would be very narrow). On the northbound side, they built a concrete room on the south end, blocking any extension. That would have to be moved.
What could be done for a long term shutdown is to extend the southbound platform, cross the service to that side and then back, and then run the two car shuttle from there to Franklin. People coming from the south would have to cross up and over to get to the IRT, and you wouldn't have the direct access to the new IND transfer. (And the IND is what you want to use, since it has the capacity, rather than dumping more people on the already over capacity IRT. So they would probably never bother with any of this.
This seems to be why crude provisions were left in the rest of the line for double tracking and platform lengthening, but some modification work would need to be done, so this is probably for a really long term emergency.