It 's a legal minefield, but I do hope they follow Delta on this. For it to really work there needs to be some kind of nationalized, standardized certification, and it has to be produced prior to bringing the animal on board.
As for emotional support (as opposed to seeing eye dogs and seizure dogs), if someone has emotional difficulty functioning in everyday situations, an airline may reconsider having that person aboard..in light of the upswing in air rage and dangerous outbursts in the air where pax need to duct tape people to their seats to prevent them from breaking down the cockpit door or defecating in the aisle.