Could it be cast in hollowed out segments, I wonder?
A hollow-cast hull would be possible, I guess, although it would be prone to warping. Sections could be a solution, especially as it would allow the modeller to use varying numbers of mid sections to produce a sub of a specific length. One could even add different bow and aft sections.
I wonder, though, if it would be more practical to instead do a range of submarine conning towers instead - those are not extremely huge, especially for diesel-electric and fuel-cell types, so could be easily placed on the table as a scenario marker, or one could build a hull to go beneath.
In any case, as I am still jobhunting and in no position to fund anything like that, it would be at least a year until I could do anything with it. That said, I'd be open to building a master model if somebody wants to give it a try.