I don’t understand [A] - why would a PARTY_PROXY need to be added as an ELEMENT anywhere in an openEHR RM structure (other than something like GENERIC_ENTITY, or whatever @yampeku comes up with)?
[B] - probably OK, and easy enough to do.
[C] - also easy.
I will note that this creeping addition of demographic data to the EHR model is likely to create problems in the long term - because it’s creating uncontrolled copies of data rather than references to anything reliable (and normally available).
Really we should just implement openEHR demographics as a versioning demographics cache…