Well, one way or the other... I bet we will see the, superior, SHIV graphics in the Atlantic. Until that time though... SH3 it is. I doubt there will be a SH5 in the near future, after SH4 more or less bombed with the fans. That divide has nothing to do with graphics however. It's sound and gameplay.
SH4 is a non-immersive sim, complete with things like a horrible interface and little things like switching the F-keys around. I hate when devs change something that was nearly PERFECT. If that can be overhauled, SH4 is the platform to build on.
Until that time, give me the second skin that is SH3 any day