At the 2016 Transport Ticketing conference in London I moderated a panel discussion on if and how we could learn from the airlines worldwide migration to ticketless which was completed back in 2008. The take away was that Airlines benefit from a strong necessity to cooperate. IATA has a remarkable power to standardize global. The local public transport is considered to focus more on easy access for the locals more than to do it the same way as the neighboring cities or regions.
Browse through the presentation here: Airlines E tickets