But there are many systems in a hospital. And as EuphoricEmu pointed out within the hospital, admits, discharges and movements throughout the hospital are still done via HL7v2 (a delimited and structured format).

Additionally, I would absolutely NOT build a new system on HL7v2 at this point in time. I would only use it to integrate with existing systems.

Also, I do know of EHR systems that use FHIR for their internal data storage format.