I'm not sure why any agency would go the smart card route for tolls.

Instead of cash, for non-regular users. There's a toll bridge/tunnel at
the Thames Estuary, for example, and while they have a transponder
scheme my usage of the crossing when I lived nearby was only perhaps
once a year. A contactless credit card seems a better bet than adding
interoperability to any particular transport smart card though.

We already have interoperable toll transponders with E-ZPass. There
are 22 different road and bridge authorities that accept each other's
passes, and some other odds and ends like airport parking. Even if
the MTA goes to a smartcard for transit I would be astonished if they
accepted it for tolls. The Port Authority already has a smartcard for
their PATH transit, and I've never heard anyone suggest using it on
their six toll crossings.

I gather that the vast majority of toll trips in New York use E-ZPass
already, since the passes are issued free if linked to a credit or
debit card, the toll discounts are significant, and there's no charge
for us occasional users when we don't use it. The incremental benefit
of taking Smartlink or whatever for the fraction of drivers that live
in the region but don't have E-ZPass would be pretty minimal.

R's,
John