Comment:

The FHIR search API does not lend itself well to some population health type queries. Some of these limitations are already being considered/addressed (e.g., "_has" parameter).

One important capability that is currently missing is the ability to search on a most recent value. For example, search for patients whose MOST RECENT blood pressure reading is > x. We can perform a search on Observation, with _revinclude to get the patient, but that search will go against ALL the patient's BP observations, not just the most recent.

This is likely tricky to design and implement, but it's probably worth the effort.

Summary:

Search API doesn't work well for population health