No that can´t be a reason. The virtual ocean needs no depth to implement submarines. You need two drawn states for the submarines. One where it is surfaced and one where only the periscope can be seen and of course the sequence between the two states. When its submerged you just need the coordinates because it cant be seen anyway, and for a wargame or simplicitys sake i think it is enough to have it dive between two or three depths (like just under periscope, medium depth and down to the limit).
You don´t need to see it speeding under the surface, because in real you couldn´t see it anyway. And for the submarine player it would just show a shadow on the flat ocean surface to know its there (somewhere below).
I think it would be a nice addition to the current mix, so destroyers and cruisers get a new role in hunting them down, and CV´get another enemy, that counters them hard since the torp bombers are of no use against a submerged submarine :-).
