We will confirm nor deny anything about the AT-AT. All I can say is "keep in mind the limitations of the 2142 engine" because that's the single biggest factor.
so will the atat carry vehicles and have corridors or be a vehicle like a tank?
I hear the developers are going to make the static have corridors or some sort of an interior, but it's impossible to correctly walk in side vehicles while it's moving in the Battlefield: 2142/2 engine. As for having vehicles, I don't know.
I had a walker moving in bf2 on a rotbundle, and when you got inside the soldier slided along the floor, and went through the cols.. I haven´t tested in 2142 on it yet.. there might be some hope for it, but can´t confirm on it yet.