What are the 5 Specializations going to be, and will DLC nations get less of them?

I know at the moment both RUS and USA have an Airborne, Armored, and Marine specializations. But what will the last 2 be? On the steam page only 4 are shown and it's Air Defense Artillery for USA and Motostrelki for RUS as the last of the 4. We know now that there will be 5 specializations but what will the final one be for each country? I know the US will receive some sort of Stryker unit, so maybe a counterpart to Motostrelki, and RU may get their own version of ADA, but what more could they add. Perhaps support with Russian rocket forces being represented?

Also, if and when the Devs add another nation, what will their specializations be? I could easily see China get 4 or 5, but what about smaller nations like Germany, France, UK, or Japan?

It's just speculation, but it's fun to think about.