Fellay is imitating the worst practices of those who got their way by being disobedient: those who used altar girls at Mass did so illicitly and after years of the illicit and abusive practice, the Vatican accommodated the practice.
It was imprudent and harmful then, and it is imprudent and harmful now. It seems to be scandalous in both instances: gross flaunting of authority is rewarded.
Nevertheless, I personally understand (though I don’t think most people do) Benedict’s attempt to bring the errant sheep back into the fold - that is why I think it nears scandal (because most people will see it as acquiescence to gross disobedience)