[raptium]

> It seemed difficult (impossible?) to pay with anything but cash

That's true and it is not convenient for visitors. Local people usually just use public transportation card (magnetic/contact-less smart card) everyday and don't have to pay with cash (you can charge the card with credit card or Alipay). Some station gates also support paying with NFC smartphones (eg. Xiaomi), and I think that's modern :-)

[pimlottc]

It's not too hard, with a bit of diligence (and a phrasebook), to get a contactless card as a foreigner. Although it is still easiest to add value with cash through one of the station attendant booths.