Unfortunately you have missed one of the key points of this game and what it is trying to achieve. This is not an arcade like experience, nor will it be turned into one games like that already exist. This game is designed to cater to a niche market and is deliberately designed to fit that niche. If and when multiplayer comes it will probably be in the following manners: 1 as and when (probably after full release) the single player experience (campaign included) is polished and in a state where the majority of the player base is satisfied. Then the dev's have said they might look into a custom battle generator for multiplayer battles, where each player can design multiple ships class with a certain budget and tech allowance and then fight against another players fleet. 2 If and when that mode can be gotten to work properly and with approval from the majority of players, then and only then will the dev's consider beginning work on a multiplayer version of the grand 1890-1930 campaign.
In regards to your request for an extension to 1945. This games timeframe ending around 1930 is a deliberate choice as its around that time that aircraft became capaable of inflicting meaningful damage on ships and as this games focus is on gun based naval war AKA the big gun battleship it was a deliberate choice on the Dev's part.
You also speak of a global campaign with clans, well the games main bread and butter is going to be a campaign stretching from 1890-1930. Clans will not be apart of it, as that diminishes from the historical aspect of the game. You will play as one of the major naval powers extant at the beginning of the game and will guide the fleet of that power right through the games end. While on this topic 'national ship designs' will be non-existant in this game simply due to its nature. For example if i'm leading Spain I might save up funds and construct the first dreadnought before Britan can which is Alt history. This first dreadnought might also be to a completely different design, than that of the early dreadnoughts of our timeline.
This is the games core and its strength, the devs know the market their appealing to and aren't really in it for the money. So multiplayer will come (most likely) in the forms i've suggested or not at all.