Well first off there's the FPS cash cow of the subsim world, U-boats, but that has already been done.
The red-headed subsim stepchild (pacific theater) was just done.
And as much as I'd like to command an I-Boat or serve in the queens navy pre 1945, these would likely attract an even smaller audience than the US fleet boats.
So my moneys on either some cold war nuke boat sim, or preferably a post WWII, pre nuke boat sim, perhaps something centering around the Korea war.
Either that or some WWI U-Boat sim.
Or the devs could have really gone out on a limb and went for..........
