Personally I'd like totally new battles. WOuldn't mind them though if they where cheap and quick to make.
I wabt to see some Barbarossa era DLC.
Also City fighting like Stalingrad with it's Factories etc.
I would LOVE to see some early on Eastern Front fights as a DLC. Where bulk of Germans are Panzer II and 38T. With T26's all over the place. I think as Shilovo was playing with aspects for Mius, expanding it a bit would be quite a bit faster to do and is well suited to what Mius is doing.
Even if it was practical to model an entire city, its not without a big budget and might run poor. Would would end up with like a map that is only a few squares kilometers. I have no idea how you could represent urban city fighting where buildings need to get cleared room by room in this engine as it is now.