That's hyperbole. The requirement would probably be something like document it and don't block it.

There already is a directive on open access to public sector data. It does not force any particular standard, protocol, let alone concrete data/interface schema. It just states data publishers must openly publish documentation, use industry standards, open data formats and protocols, and publish machine readable and processable data.

Of course there wonʼt be a mandate on exact API endpoints or data structures for every kind of service anyone could possibly create. That would be an impossible undertaking even for a bureaucracy like the EU.