Does the scheme mean I can travel abroad purely to receive medical treatment?
No, not generally if the purpose of travel is to receive public-paid treatment – there are separate systems for that. For example, in the UK any travel for hospital treatment has to be pre-authorised by the NHS, which has its own rules. The extended E111 system intends that people with European public health cover should not be discouraged from EEA travel just because they might need incidental treatment.