I could see them gradually turning disfellowshipping into an unwritten rule to reduce litigation. The Watchtower's expectations don't have to be spelled out to be quietly enforced through peer pressure. Aren't weaker members already 'semi-shunned'?
Also, even if they did this, there wouldn't be a clear explanation or announcement of "no more shunning" that would shock people to their senses. There would most likely be a convoluted legalese "refinement" of their understanding, written by the legal department, that no one would fully understand or be able to explain. Leaving the door open for further "refinement" in the future. Similar to the overlapping generations explanation.