This is what it could look like once modded/DLC'ed.
The immense variety of ship types in this era can lead to a completely absurd tree with countless branches : this would be bad. But so is the excessively simplified tech tree the devs offer us. The land tree and air tree are good, and one of the reason they are is because they offer easily accessible variants. Instead of carrier planes, tank destroyers and self-propelled artillery having their own trees, or branches, they became auxiliary researches to plane and armor techs.
Ships have no equivalent.
Just imagine if it looked like this :
The much debated question of Panzerschiffe and Coastal Battleships could be solved easily if they were made subclasses of Heavy Cruisers. PBs would be more costly, but gain increased firepower and range, while CBBs would have a dramatically reduced range, but acquire increased armor, firepower and a bonus while fighting in coastal areas.
Watching yesterday's world war wednesday and listening the player explaining how, despite his best efforts in fortifying the border, the Soviets could easily launch amphibious attacks made me realize how the Scandinavians minors, which would be among the most played minors, would benefit from such a change.