[CB..]

i agree the inclusion of even small RPG details can have a huge impact on the immersion and feel of a game--the crew management system in SH3 does have very minor rpg hints--

i would love to have some sort of officers mess to spend time in imbetween patrols/missions---perhaps modelled in full 3d like the sub interiors with animated sub commanders and a set of pictures on the back wall--as time goes by the number of pictures (of those commanders who have been lost) increases and the animated commanders in the mess change---this wouldn't be fully RPG in any major way BUT it would create
a good emotional link between patrols---and some sort of sense of story line as commanders died and were replaced by other new faces--bung a bit of music in there (and a multiplayer chat room for on line players) and you've got quite a nice way to link each patrol--really just a update of the old AOTD officers mess--
run a few random AI captains careers and show their results on a board in the mess--even if this didn't actually occur in the game engine it self and was just calculated at random for display in text from on a notice board -this would create a minor roleplay nugget for the imagination to enjoy--

allowing the player to check the notice board and wonder if "old such and such" has survived--

of course you could even have a mini game allowing you to play chess with your crew on long patrols--and the league table displayed on the sub notice board--completely optional of course but fascinating--

randomised letters from home --newspapers etc all would help create a role for the player enhancing the potentail immersion--