If it was part of the right solution, it would not take 20 years to come up with a regulatory fix. It is in nobody's interest (except perhaps China's) to have this fleet remain grounded for a long time, assuming that it is basically a safe aircraft. It would help if the political situation were more normal, but aside from that everybody knows what is going on and what doc fixes are required for this "one time situation". That is much easier to process than regulations/specifications that are supposed to guide several decades of future development.