Not like we are in any rush. We don’t really need dedicated maps until we expand to WW1, and the tanks perform well enough considering their age.
As for WW1 tanks, any WW1 tier would almost certainly include the early to mid inter war era that isn’t currently depicted in game, so we have those tanks as options.
There are also a few WW1 (or vehicles built prior to 1920) that could be added. For the US at least, there is the Holt Gas Electric, which was armed with a 75mm gun from what I can recall, as well as the Holt Three Wheel Steam tank, which also mounted a 75mm gun. Also possibly the Ford 3 man tank, which was intended to be a better FT. It was built, and pictures of it do exist, the problem is, we don’t know what it would’ve been armed with. Likely would’ve had the same armament as the FT at minimum, though there is reason to believe it could’ve been had a bigger gun. Also, there’s probably a car or two with a .50 cal that could be added, seeing as how we already have a tank with the .50 as its primary armament.
Don’t know much of German tank development, but the K-wagon is a possible WW1 addition, being almost complete before the war ended, though it would probably be in a higher tier if the 2C is anything to go on. The LK ll also had a variant armed with a 57mm gun to my understanding, as well as a prototype armored car armed with a 20mm gun. Also a big wheeled tank, but it’s armament might be too weak to justify implementing
For Russia, the only real tank they have is the Tzar Tank, at least as far as vehicles prior to 1920.
This isn’t an exhaustive list, however. I haven’t touched France, and they made quite a few tanks. Nor does this consider the SPGs developed during the war, which there are quite a few.
It also doesn’t consider interwar developments beyond the most early examples, so there’s bound to be a few with comparable performance to WW1 designs that can be used.
And all of this was with a casual search. I’m sure a dedicated hunt could turn up far more designs.