I still think however the questions are for the regulators - any expectation that commerical companies are going to carry out experimental research which the regulators could simply refuse to accept (which is certainly the case which has occured in my own industry) is naive in the extreme.
Ultimately you are right, the regulators are the ones who have the final say, however there is a lot of precedent for operators liaising with manufacturers to get Flight Manuals tailored for their unique operations or for specific circumstances (operating off ice/snow or take off distances/speeds for challenging short runways). If the industry as a whole had said 'We need guidance in the manufacturers Flight Manual for volcanic ash operations'', then for a price I am sure the work could have been done and we would have developed a better system than the one which caught everyone out last week.
The 'no ash' requirement was never going to be defensible. Possibily it was just a political stance taken to try and force the industry to think about it, possibly not. Either way it will be interesting to see NATS and the CAA defend the position they took.
The defence is easy. ICAO documentation, of which the UK is a signatory, paraphrasing said 'Volcanic ash then no IFR flights'. The UK had not filed a difference with ICAO and therefore was bound by it, regardless of whether it was the best option or not. There are IMHO better options out there (Alaskan procedures look a great starting point), which in slower time could be developed and agreed as international policy. But again it will boil down to someone doing the research and development and putting in the resources to convince the regulatory world that it is safe. I am sure the UK authorities will want to be part of that process, if only to ensure that lessons have been learned and a better set of procedures is available for next time. It may also mean improved infrastructure is required (LIDAR and more readily available sampling aircraft), but then that will be subject to a cost benefit analysis and political will.
Time will tell !