What? Life after Silent Hunter???? I don't want to think about it!
If they ever to a modern one, the problem will be how and where to set it. There hasn't been a conflict that could make a good bases for a conflict (the best that comes to mind would be the Falklands, and that's pushing it). The only way is to go hypothetical like Harpoon.
It's best to stick to WW2 era subs as there is more historical data to work with. A new game engine for the pacific and atlantic would be a good starting point, maybe some AI subs and the ability to play different countries (British, U.S., German, Japanese, Italian and so on). Doing it by add on or providing the bare bones of it so modders can do the work for them.