While I appreciate the need to Communicate about a conversation, there are cases where it would be beneficial to have a conversation/dialogue using the FHIR API between a patient and a provider/organization/payer in a way secure messaging works on portals.  There is no standard way to do that from patient facing apps that use FHIR to communicate with providers and payers.  Communication could easily support this use case.  Recommend allowing it.  Recommend changing: "This resource is a record of a communication that has occurred. It does not represent the actual flow of communication." to "This resource is a record of a communication that has occurred or is occurring. It does not have to represent the actual flow of communication but in some use cases could (for example secure messaging between provider and patient).