There's a bit of a difference between a request for a height / heading change (at least partly) for the comfort of pax and a 'must have' change because the current heading / height is not going to be 'safe' after another n minutes (where n is less than 5).
My scepticism was not primarily on account of ATC consequences anyway. I'm much more concerned that systems on board aircraft on scheduled routes would actually add value in practice. Potentially, a lot of cost and extra weight that could not be recovered / removed when there is no ash risk, combined with little real benefit when it does get used.