The problem with it though is it would seem you still need another option available. Not everyone has a smartphone. Presumably they still want to service those people, so they have to provide some other option. The scan on/off system works for everyone, and it could easily be extended to busses. It'd work the same as a station, but you do it entering/exiting the bus.

I could see the issue with stations that don't have gates, but again, they should be trying to service everyone, including those without a smart phone. They have to add something to those stations I would hope and assume. It might as well be a scan point —which could be something besides a gate.