It's great that Graviteam are actually interested and taking this seriously, most large game companies probably wouldn't even respond.
Another alternative maybe to approach Ilan Papini developer of the Virtual Sailor series which already has good environments, weather, ocean etc and is fairly easy for the "average Joe" to add models/units to. We could ask him funded via kickstarter to add in the additional technologies eg sonar, radar, hedgehog ,aa guns, depth charges etc needed to turn VS into a WWII subsim. His strength is probably not in enemy AI as he is not a game developer per se but it could work as purely a multiplayer game with subs, destroyers & convoys all under user control with the addition of the technology of the time.
This
old thread of mine may also add some ideas into the mix.