Clear benefits would be:
- Easier and more accessible (ticket machines aren't in all stations), tourists would appreciate as well
- Reduce the amount of paper tickets and machines at stations... environment :))
- The value in the card and recent trips could be seen straight from wallet app
- More durable and reliable than ov-chipkaart, as the phone pushes the signal faster
A good example can be seen with the Suica card in Japan, where all of the above points are met: https://support.apple.com/en-us/HT207154
Allowing your bankpass is not a great idea due to privacy concerns ; different countries use different networks ; not everyone has a debit/credit card and not all countries issue contactless cards... Bank cards will create confusion in my opinion