Im pretty certain that SHV is the last in the franchise for the forseeable future. Im under the impression that Dan and co had to twist a lot of arms to get a green light for SHV.
What you are suggesting would need development budget of Fallout 2 proportions, aint gonna happen for a niche Uboat sim and definatley not on Ubi's watch.
No harm in dreaming though.
On a side note, there is one glaring problem with an online SH campaign, Time compression.
For it to work, everyone would have to either be forced to play entire patrols at 1x TC or you would need a spawn/ teleport function.