It's a neat proposal, but you would need to designate only one (no more, no less) of the RF-capable devices (credit cards, transit cards, smartphones/watches) on your person as identifying yourself for transit usage; otherwise it might over- or under-charge users. That would not be easy to explain or enforce to the general user base.
The standard that I believe the better agencies are striving for is 'open payment'; you do need to tap one of the above noted devices, but there's a large selection of such options and you're free to use whichever suits you.
The standard that I believe the better agencies are striving for is 'open payment'; you do need to tap one of the above noted devices, but there's a large selection of such options and you're free to use whichever suits you.