Just a bit of trivia:
I went to high school with John Ratcliff, the author of 688 Attack Sub.
http://en.wikipedia.org/wiki/688_Attack_Sub John, his brother Tom and I used to hang out together and we were known (scorned one might say) as the "ubergeeks" of our school.
If UbiSoft wanted to do a SH5 in WWII Pacific environment, I'd first say, add better AI, wolfpacking capabilites and fix some of the "hard coded" problems with SH4... Then ask the RFB, RSRDC and PE developers for permission to incorporate those mods into the new edition. Why? Because if realism is one of the new design goals, those mods would save the Ubi devs thousands of man hours and at the same time, show recognition to the modding community that produced them.
One of the best "realism" sims I ever played was Jane's AH-64 Apache. IMO, it "hit the nail on the head" in all aspects for realism, historical accuracy and the flight model as well. No reason an SH5 couldn't do the same...