I don't know how well something like this would work for an international website or service. There are a lot of challenges, like for example the centralized authority responsible for managing and creating new IDs could abuse the service. It isn't fool proof.
Not really, unless you think of PayPal and Stripe as the "centralized authorities" of credit card processing. It's still a system with multiple authorities/centers of power; you'd just be paying a third party for the convenience of integrating those multiple authorities into a single layer of abstraction. If you're worried about the aggregator somehow subverting or altering your requests, you can always cut them out of the transaction.
When a single entity is responsible for managing IDs that governments provide it is ripe for abuse still. I'm not saying it couldn't work but these issues would need to be worked out. I'd rather see a decentralized solution that allows users to pick which IDs to accept, etc.
