In the base game, we can build anti-tank, SPG, and anti-air variants of any tank, bar the great war tank. This makes sense, as there are many examples of specially built tanks for these purposes. However, one thing that is not yet represented, alongside armored cars like the Sdkfz. 234 Puma or M8 Grayhound, are motorized and mechanized variants of the same kind. For example, the US had the M16 halftrack, with 4 .50 cal machine guns, or the M3 GMC, with a 75mm cannon. These could easily fill the AA or AT slot, and just fill in the rest for the sake of having all. Heck, you could even restrict it to just mechanized. Even an armored car could have a specialized variant, such as the 234/4 Pakwagen.