Like Ducimus stated, no big publisher will get involved with a historical WWII sub-sim.
If anyone, Paradox might take a crack at it. They're are currently working on a naval game (actually, Turbo Tape Games; Paradox is publishing), but even that is stated to sacrifice some realism for gameplay (not a bad thing imho, but it's not what SH is about). And it also focuses on larger scale naval engagements, not the niche-within-a-niche that is WWII (or any era, really) submarines.
I guess there's Stardock as well, but I don't see them getting involved with naval games anytime soon.
Think there were some rumors going around about
Valve doing a sub-game, but that was based on the fact that at some point in the distant past they worked on one for a bit. Not exactly compelling. And probably wouldn't be a sim.
And there's Akella. They do quite a few games that prominently feature the high seas... not sure how likely that is though. Their offering that comes closest,
PT Boats, fell a little short of expectations, so they're likely burned on the genre as well.
Not a chance in hell Eagle Dynamics is even remotely thinking about submarines at the moment. Maybe Sonalysts could pull something off, but again I would expect something along the lines of Fleet Command/Dangerous Waters... never know though, they are far from out of the game.
