That is true, HL7 FHIR (which is basically "you shouldn't call it HL7 v4") is supposed to be the future.
This also means that at this point, virtually no system supports it as such, and the standard is still in a moving state.
At this point, HL7 v2 is still the most used standard within hospitals, if you want to communicate with labs, financials systems, scheduling, etc.
That being said, it'd interesting to add support for HL7 FHIR in GNU Health, but I think it would be a mistake to make that priority #1.
Starting November 23rd, wife and kids will be away for 3 months, and I plan to be able to spend much more time on this.