Probably quite slim chances.
One of the most striking things about CofC is just how reluctant Raymond Franz was to leave the GB and the organisation. Despite all his doubts and differences with JW teaching and policy, he actually wanted to stay.
Sometimes I think Franz is misunderstood as having decided to leave JWs of his own accord over a "crisis of conscience" but that's not what his book actually says. He tried very hard to evade expulsion, but he apparently had some powerful enemies on the GB, and in the febrile post-1975 atmosphere they were determined to get rid of him.
It's an unusual set of circumstances that's probably unlikely to be repeated. If there are GB members with doubts or differences they are likely to stay where they are unless very strong (probably personal) motivations compel them otherwise.