The problem, even with a spinal cord cut intentionally and carefully, is that the surgeon has no way to know what connections in the head go to what connections in the body. Our nervous system-brain interface isn't a blueprinted thing at birth, our brains are actually born with no knowledge of the nerves running through our bodies. Our brains and bodies learn to interface with one another via "neural pruning." The brain is born with a bazillion* neurons, far more than it needs, but this is to account for all the possible nerve connections. Then, as the body grows, the nerves send signals to the brain, and those neurons that don't receive signals die off, leaving the neurons that are properly wired into the body. In other words, our brains grow by natural selection.
So how is a surgeon supposed to wire up a body to a brain that hasn't grown into that body? How is a brain pruned in childhood to interface with a body of certain dimensions and nerve-wirings supposed to interface with a body of completely different dimensions? It's not just a problem of lining up the nerves in the donor body with the right connections in the patient's head (a seemingly impossible task in and of itself), its the fact that the nerves in one person's body are going to be a very different set of wires than those in the the head. Many of the major nerves will match, but the signals from those nerves will be very different.
I wish this researcher the best of luck, and I imagine we will benefit tremendously from the new information we get from this research, but I suspect the final result will simply discover what the next challenge is to performing a successful head transplant.