Old-style cell blocks make for interesting but challenging interior spaces. This is what it looks like inside SCI Pittsburgh:
Fortunately in this case, the building has great windows and it is one long building (sometimes they would layer these next to each other), but for any re-use but a monument or museum, I would think you would need to basically remove the cells and create large open spaces.
What you would get is something much like Hunt Armory or Mill 19. At Mill 19, they are basically building new buildings within the shell, and there was a proposal like that for the Armory too. Or you can make use of those large open spaces, such as the approved (but stalled) plan for a skating rink in Hunt Armory.
Off hand, I could see doing some of all of that with this building--some parts could be left as cell blocks for monument/museum purposes, some could be opened up as event/recreation spaces, and some could get the building-in-a-building treatment for apartments, offices, or such.
I might note I believe the closure plan includes a substantial chunk of money for "mothballing". I don't know exactly what that would entail, but I would hope it would be done with an eye to long-term preservation for future re-use projects.