But aside from that, I don't think that means you only need one state to get unified transit off the ground. Every locality that operates public transit would need to be on-board. (Even if CTA started taking payments via Illinois toll road accounts, me swapping my Colorado toll road transponder for an Illinois one wouldn't help me use RTD unless they're also on-board.)
I think the bigger implication you've pointed out is that if toll road & public transit payments become integrated in lots of different jurisdictions, it could come along with free multi-jurisdiction transit integration via the existing multi-jurisdiction toll integration. But it would still require that toll/transit integration to be built out in lots of different places first.
So really, you only need one state to adopt your unified transit fee idea.