I'm personally not so interested in a WW2 version with carriers, because I'm really fascinated by the period of naval warfare from around the RJW to the end of WWI. But I must agree that the SAI campaign expansion is just amazing. I'm playing the 'Germany Stronger' campaign, and as I play I'm reading Paul Halpern's 'A Naval History of World War I.' The book has given me a much better understanding of how the opposing forces operated, or tried to operate. Sometimes we forget that it wasn't all Jutland-type battles.
One thing I wish SAI had was a slightly less rudimentary map. I love the ship graphics, and I understand that the focus here is on historical accuracy [as it should be]. But when I send my BCs to bombard some target along the English coast, I wish my sailors had something a bit more appealing to look at. Surely it would not take much to spice up the map just a bit. Perhaps in a future upgrade?