@trberg Odysseus worked with MarkLogic a few years back and successfully re-created OMOP CDM as a graph. It is actually not that challenging to do it, and it was a very interesting POC. The real challenge is that once you have done it, none of the existing OHDSI methods and tools - which are all relying on SQL - would work. Even though MarkLogic experimented with enabling SQL on a top of their solution at the time, the SQL support was a bit more limited that required by OHSDI.
Re-creating OMOP in a document style was very interesting - PERSON as a document was the concept we experimented with. Document format does offer an interesting combination of data harmonization plus some flexibility for not yet harmonized domains.