Personally I don't see the point in a modern subsim... current subs are for intimidation regarding missiles launch and not much else, and with so much tech, would it even be challenging or exciting to hunt, position and fire torpedos like the good old days with low tech and duds? I think I doubt it... :hmmm
I would be happy with:
- a full WWII historically accurate campaign (in several theatres of the war and possible playable factions (Germany, US, British, Japan)(would demand a lot of work, though), providing plenty of scenarios and zones to patrol.
- or maybe a German one until the end of the war, with a follow up & made up story of our character being secretly recruited by US or USSR to fight an hypothetical conflict between the two powers of the Cold War for some time... wouldn't be so "Cold" then, nor historically accurate, but would provide a feasible scenario to those of you that are fed up with WWII and would want something else. Not so interesting, though.
Anything different than that (meaning: modern subs), it's a clear no go for me. But that's just my personal opinion.
Good graphics are an important factor and any engine out there gives the ability to lower the settings to those who don't have the full power on their PC's. Not only the game should look good to us, but would attract more people to buy the game later. Not saying it should be Crysis 1 like, but I wouldn't accept nothing less or equal than SHIII on highest settings... I would want some nice details when the ship is hit and goes to the bottom and take some nice screenshots/videos that would help promote the game a lot.
After the basic stable version and beta completed, it would be added on Steam (by Greenlight, probably), a lot of people would buy it full price and on Steam sales. (EuroTruck Simulator was Greenlit, for example, and is doing nicely and selling a lot more than it would if it wasn't there).