That is a fascinating hypothesis.
Not only could dogs carry a pretty good load over rough terrain, there are other advantages.
Dogs' ears and noses will also inform a person if there are any other critters around, something I think would be quite nice to know if one is living in a rural environment. I know that's great comfort to me when I'm walking in the woods alone at night.
It may well be that Homo Sapiens was assisted in it's early survival by the extension of it's sensory system by borrowing dogs.