Interesting-in my game the Central Powers went crazy with naval units but even with some bad luck, they were eventually able to gain control of the Mediterranean and the Atlantic, isolating the US. Germany was pushed very far back, but some Allied mistakes enabled Germany to recover and push the Allies all the way back though France. Russia surrendered, and Austria Hungary went crazy eating up Italy, starting an invasion of North Africa, pushing into the south of France and being the main force on the Eastern Front. The British, after losing their navy, started pouring units into India, defeating the Ottomans, but not quickly enough when the game ended prematurely (the board got all messed up). You have some interesting ideas, which I will comment later. My game was not actually on a real board (the game is so expensive, but a real one should be arriving soon), but a piece of paper with the map printed on it with mostly World War 2 units and a few World War 1 units bought online used. Also, your post have say Central Powers instead of Axis.
Adjusting Ship Costs: I think this is an interesting idea, although it might not be historically accurate. This requires more pieces though, which the game is lacking and it’s very hard to find and get them online.
Submarine Rules: This probably means destroyers should be added instead of cruisers getting the special abilities you have described, but there are no pieces. This is not historically accurate, so I’m not a fan of this.
Restricted And Unrestricted Submarine Warfare: I like this idea, so I don’t have much comment. You should also introduce this system for the Mediterranean, probably for countries such as Italy, France, and Britain.
Defensive Dive: Good idea, but maybe the dice roll should only go down based on the amount of destroyers in the battle, but again, they don’t exist. Although this idea still works best with destroyers instead of any surface ship, another good idea is that for every surface ship there is, one submarine can’t roll the dice on a one to one basis.
Aircraft Combat: Whilst your ideas are interesting, I don’t think it is impossible to challenge the air, unless your opponent invests twice as much in aircraft as you do, and if the opponent can also maintain strong land armies, the game is probably already lost.
Artillery Neutralization: I have absouloutely not problems with this whatsoever! It’s accurate, fun, and intresting.
Overall, all these ideas will make the game very fun. Your truck idea is also quite interesting. I wonder what pieces you use? Thank you!
There was a long topic several years ago talking about many potential changes to the game: