I just returned from Copper Canyon (on motorcycles) and it would seem to be perfect for a Sportsmobile. It is paved to Creel and then graded dirt roads to Batopilas and Urique. There were many trails that were clearly 4x4 trails, poor by any description. They were even tough on a motorcycle.
You could pick the level of adventure and you would be sure to find terrain to match.
Copper Canyon (or Barranca del Cobre) is a Mexican National park and is the big brother to the Grand Canyon although I would position it as different not actually better or worse.
This time of year, it was cool at the bottom and snowing at the top. Summer is supposed to be hot at the bottom and beastly hot at the top.
That said, many of you are from places that get hot in the summer so perhaps it won't be as bad for you folks:-)
Services are plentiful although basic. There are quite a few Fords trucks in that area, it was the most common brand truck we saw.
Spanish would be very helpful if not essential. The people were uniformly friendly although the English was sparse. My second year spanish seemed to do fine although we didn't speak on politics or philosophy.
I met several people in truck based campers as well as many other US based motorcycles groups, it would seem that the profile of CC is growing and it is seen as an alternative to the areas that seem to have crime issues (Baja has received poor press in the last year).