I mean, it's VBS Blue or whatever they're calling it. I really doubt Arma 4 will have that functionality. There's a lot they cut from VBS to the Arma series to make the games borderline playable. You don't need a poorly rendered planet for a milsim game. You just need a large, slightly less poorly rendered environment.
I love Arma as much as the next guy, but I'm not getting my hopes up. And if it does turn out that the next Arma has the entire planet? I'll be very impressed.
They could barley run Altis map since, engine is so backwards, and all map assets are processed on your PC, so I am skeptical, that they could pull it off. But then again Arma 3 is the most advanced shooter by far.