I think asking the airlines is asking the wrong people
I can see why the questions about acceptably safe ash levels went unanswered. From the safety standpoint the manufacturers surely are the right people answer that question, NOT the operators.
The airlines can answer a lesser economic/commercial question, such as 'how much wear and inspection can you live with?'
'How much gunge is up there, what is it composed of and where is it?' is surely a question for the MET people.
'Can you accommodate routing flights around this gunge?' is a question for the Air Traffic Services people
I believe there are also questions to look at regarding pax compensation, insurance and priorities for travel.
I don't think the existing compensation rules make much sense. People who are stranded away from home clearly need compo for accomm, but people who are merely delayed in their home country probably don't. I don't see why airlines should be compensating for weather, including ash, unless there is a humanitarian need or the journey has started but hasn't been finished.
Insurance cover that's void is clearly a problem to address- otherwise people quite rightly won't buy it. We need an insurance system that's functional, then the airline funded compensation problem is a lot smaller. Actuarial and underwriting systems exist so I cannot see why we have to allow insurers to weasel out.
Finally although I'm a lucky person with a booking which replaces a kangaroo route trip scheduled for 2 days ago... I can't help thinking that slavishly honouring bookings for flights that operate at the expense of people who were unlucky enough to be on cancelled flights is a worry.
Maybe as a minimum people with good bookings could be asked if they will give them up, possibly in return for an inducement such as an upgrade or money. That way people who urgently need to travel might stand a chance of getting on, especially if they (or their insurers) are content to pay extra.