The super high roof is not capable of carrying loads from what I understand. That would not allow an air conditioner for starters. I assume solar could be fastened to the gutter system but I am not sure about other things like skylights, Maxxfans, satellite dishes, etc. I'm not sure why one would want a super high roof since the interior height is 6'-3" already. Maybe a tall person but it certainly would not become a standard either.
The other thing I haven't investigated is the load capacity of the 4x4. I read it was less but don't know how much. Advanced RV is already anticipating this in lightening things up. Their stowable table for instance is being made from a lightweight composite material. They are developing optional running boards instead of the fiberglass skirts. I believe they will be lighter.
If it becomes a default platform it will be because that is what customers order. There technically is no default with Advanced RV other than they are dedicated to building on the Sprinter platform only at this time and have a basic plan (which I am modifying, BTW). I'm not so sure about popularity and I live in Minnesota but don't drive in the snow if I can help it. The whole idea of a Class B is to get away from the snow.
If I knew more about the 4x4 and wasn't so already antsie for a new RV I might have waited and ordered one, regardless. My wife, not so much. She won.