Valid points. But: with the paypal method, the user is reliant on merchants. No button, no automated Revolut payment. In Europe, this market is crowded. They probably need a new business unit for this, processing payments for merchants. At a large scale.
The plug-in idea on the other hand solves a problem from a user’s perspective alone. Disposable cards make proven ways to fill in card numbers useless. The first step would be to make it easier to copy card details. But a plugin would allow to enter all card details, name, number … in one step.
While the “Pay with Revolut” button would be a diversification of their business model, probably relevant for both their business and consumer customers, the iOS “fill in” plugin is way easier to realize. It dips into the operating system’s share menu and just fills in a form, independent from merchant implementations and PSD2-compliant payment processing.
That’s the beauty. It’s a simple solution for a real usability problem. And it could be done without partners.
Am I expecting them to integrate this in the foreseeable future? Probably not. I also have security concerns. Still a clever idea.