may i suggest a solution i have not heard yet
--- flight plan all flights BELOW 20k feet till clear of ash. I KNOW .lots more fuel but if worked out and tickets charged accordingly there yiou are . even long haul flights could be planned to climb after cloud and continue . most have the fuel capacity . i stand back and await brickbats
Good theory, if it weren't for all recent Met forecasts showing no significant ash ABOVE 20k.... It's the getting up there that's at issue. But I agree, If you can get up there, through the mess fast enough, and "blow out" the muck, you're good, till you have to get through it on descent....