One big limitation of this standard is imaging data. X-Ray radiographs, MRI scans, PET scans, etc are not part of the USCDI standard V1 that'll be available to US patients. The current story for getting these scans still sucks and isn't close to being actually available to patients in the US. The best you can get is a set of DVD's containing that stuff, if you are lucky.
The problem is that the protocol used by imaging devices (DICOM) is ancient, and connecting with a DICOM server is a pain. There is a sort of modern standard that I've heard talked about called DICOMweb, that I think will be hooked up with FHIR and be made apart of the USCDI eventually (probably). But we still aren't very close to being able to see X-rays on our phones.
Also, one funny anecdote I've heard from working in this space is that some doctors do not like the Clinical Notes story (https://build.fhir.org/ig/HL7/US-Core/clinical-notes.html) since it means that their personal notes about their patients will be made available directly to the patient, something that was not possible in the past. Doctors often write down their real thoughts about the patient in there and can say some things the patient might not be happy with.
The problem is that the protocol used by imaging devices (DICOM) is ancient, and connecting with a DICOM server is a pain. There is a sort of modern standard that I've heard talked about called DICOMweb, that I think will be hooked up with FHIR and be made apart of the USCDI eventually (probably). But we still aren't very close to being able to see X-rays on our phones.
Also, one funny anecdote I've heard from working in this space is that some doctors do not like the Clinical Notes story (https://build.fhir.org/ig/HL7/US-Core/clinical-notes.html) since it means that their personal notes about their patients will be made available directly to the patient, something that was not possible in the past. Doctors often write down their real thoughts about the patient in there and can say some things the patient might not be happy with.