I have been considering this question privately for some time too. My own particular anoyance is that islands are completely surrounded by a single sea zone. I think many islands should have more than one sea zone touching them. For examnple, I think the Phillipine Islands should at least have an Asian side and a Pacific Ocean side. I think Japan should have one sea zone with Korea, one to the south and another to the north and east. While we are on the subject, I also do not understand why the sea zones have to end coincident with several (most) adjacent land borders. This forces many strategic manuvers and I would appreciate some more tactical flexibility. However, I see that the game is very delicately balanced (at least until someone finds a real deal breaker) so such tactical choices may make the game difficult to balance.
I would be interested in a more accurate Pacific map, including the expansion of the Pacific Ocean to its true size. The biggest problem I see is that it may become unplayable for the Japanese. Two factors that made it tenable for them was the hidden movement (for of war) of sea forces in general, and the benefit they received from their attack on Pearl Harbour.