To answer your question, there is probably not one golden truth.
Once that said, regarding an international delivery of such journey planner, we truly believe that "yes" this is not only a potential, but a probable roll-out to come.
The issue is for the solution provider to be in position to integrate the different mobility offers in a single place. It takes time and connections, but it is largely feasible from our perspective.
Regarding your other question about the payment (through the solution provider itself or through third parties), there is not a single answer :
1. it is more likely that such a journey planner (if international) would have to go through the payment system of each mobility provider. A bit like SkyScanner for example.
2. whilst being a crowded space, no one has found yet the value proposition / business model to be attractive enough, to become the center of all systems, and thus being strong enough to centralize the payment for all the others. But it is not because it has not happened yet, that it will not happen. Reversely, the operator who would find such a value proposition, would make the journey planner profitable and therefore quit an "information only" positioning. It would be the Tripadvisor or Google of multimodality: being both neutral but monetizing the fact that they have a dominant connection with consumers.
As in every market, it is not a question of offer. It is a question of demand.
An offer is never dominant except if reaches a dominant part of the demand !
I do hope it answers (at least partly) to your questions.