Ha ha, gotta love even vague spoiler hints. Models of ships, that sounds intriguing. I wonder if this opens the door to the American AA cruisers.
I don't have any knowledge of the game beyond the DDs and posts around here. I'm extrapolating from previous evidence they've presented. I could very well be wrong, and instead podcat has cut a deal with My Little Pony to have sparkly-pony based capital ships. My Little Pony: Blitzkrieg is Magic!
Why can't we just do it the way this is often done: by tonnage and purpose. For example, the modern definition of super carrier is dependent upon tonnage. Thus, for example, any ship above 60k or 70k tons would be a SHBB. The reason why we SHOULD differentiate between SHBBs and normal BBs is because many of these nations were fielding them (or planning to field them) along side their conventional BBs. That is also the same reason can't say: anything post 194x year now counts as a SHBB. They were designed alongside modern BBs to serve as upscaled force multipliers, and thus fit into a category of their own.
Because the trend in battleship design favored larger ships over time. With the exception of the Lion and Alsace classes, everyone else who was interested in battleships were interested in going bigger. With no treaty limits and no end to production in Germany, Japan, the United States, and the Soviet Union, the most technologically advanced BBs for all of these countries by 1944 would have either met Yamato's size or have been considerably larger and better armed. Not to mention that H-44, Montana, and Sovetsky Soyuz would all have been at least marginally faster than Yamato.
So, there isn't really a need for a SHBB ship type if the timeline for battleships gets extended, because Yamato's specs would have become the norm or even a bit under par among battleships built by 1944.
Lion and Alsace would be more or less battlecruisers in a world where Montana, H-44, and Yamato are the pride of the USN, Kriegsmarine, and IJN.
The best thing is that this general fits for almost ANY SHBB that was historically being imagined. Even the Tillman classes designed in the 20s, long before most nations started planning their own SHBBs, would fit under this definition.
But why have a SHBB unit at all if ships continue to get larger, have heavier armament, and get faster over time?
I don't see the problem. Weight is not an issue since we are only classing above a certain weight (as we do with SCVs). Furthermore, for things like guns we can just use tech levels, which WOULD accurately reflect what they were capable of at the time.
So why have a SHBB unit at all if tech levels will take care of it?
The same way that if the Treaty of Versailles hadn't existed Germany probably would have built up a substantially larger conventional surface fleet with BBs and CVs more comparable to the German Empire's Dreadnought Fleet that was challenged in size and power only by the RN? Treaties matter and affect how history unfold. They also affected ship building significantly.
Of course they had an effect. That's why I'm pointing out that the Washington Naval Treaty and the London Naval Treaty ensured that, while larger battleships could have been designed and built from 1925-1936, they weren't. This resulted in a generation of warships that were smaller, less armored, and less well armed than any of the signatories could have actually built.
Except they aren't logical. It is completely illogical that one kind of ship magically can't increase the amount of armor or its engines - only its guns. Especially when every other ship in the game can. Besides, why should we allow this "tech skipping"? We don't allow anyone to build OP tanks or infantry that get made obsolete over time. SHBBs were only better than BBs in the first place because they were bigger, leaving space for more engines, more guns, and more armor. That we magically can't improve upon them by applying new techs and new designs that improve efficiency and add even more is absurd. In that sense it both spits in the face of balance and in the face of historicity.
SHBB can't increase its main armament. It can upgrade the following items: AA, RADAR, Fire control doctrine, command decision doctrine, ORG, and morale.
How is it unbalanced? Other than who starts with the tech in 1936 (which seems historical to me), anyone can grab it quick and try to play catch up. I've invaded Japan as the Soviets using SHBBs in 1945 without too much difficulty.
You say that the implementation of SHBBs isn't historical, while I would say that having a SHBB unit in the first place isn't historical.
The problem is that in many cases SHBB weren't just "different" models. Think about it this way: there's a reason the US built Iowas instead of modernized Tillmans.
I'm not sure we are using the term model in the same way. If you look at the DDs that have screenshots of tanks, you'll see what they call different models. You can upgrade an existing model, like a Panzer III, with better stuff, and you can also unlock new models of tanks, like a Panther. A new model is not a modernized anything. Its an entirely new thing. But we haven't seen a DD about the navy, so who knows what will actually happen.
also ground based planes could wipe out carriers airplanes. Its limited amount of those on board. and more cannot be delivered there instantly behind thousands of km away. I think CV fleet would go to bottom pretty fast from BB/SHBB fire in that case, so they are not worthless at all. If other side has just cruisers and other small ships to protect CV:s and other goes with BB:s.. 
