GDPR only requires erasure of personal data on request, where "personal data" is defined as information relating to some identified or identifiable person. Machine learning models trained on personal data aren't going to be personal data themselves.
Machine learning models leaking private information is a real problem though, unless mechanisms to ensure something like differential privacy are applied. Those approaches may still be too theoretical and hard to reason about for many machine learning practitioners. Will be interesting how that plays out.
Well, unless they can be used to identify the person.
But we are (reminds me of black mirror...) entitled to having knowledge and memories. Corporate entities will start to claim that you cannot ask us to remove our memories (for example, identifying people in images).