Union types would be an incredibly useful extension of this.

Indeed! pysonar2 uses them with success.

Greece has several such open API endpoints for validating information, including VAT/company number, the equivalent of social security number, whether your personal tax returns have been processed, whether you were admitted to a state university, and so on.

For most of these services, all you need to access results is a subset of the relevant information. There is no requirement to register or authenticate, but they do seem to have crude forms of rate limiting in place.

I can only imagine his mother as Ayn Rand.

More likely his mother got tired of his self-centred freeloading.