Bespoke front-ends and UX have never been open source's forte, but shared serving technology running behind the scenes has been wildly successful.
Health care seems like a good fit for that.
(Said as someone with clients in insurance, and well aware of how quickly data interchange can embrittle an architecture)
HIPAA greatly complicates a lot of data sharing because of appropriate data privacy issues.
Obviously, driven by the reasons and pressures you outlined in your parent comment. (Everything is sold and certified as a system, rather than a component)
It seems like there's an opportunity for OSS to eat shared functionality, that no vendor particularly liked implementing, and then allow for closed source UIs to be built on top.
E.g. EMR store/server being the open product, with {insert your preferred front end on top, for your specific use case}
In insurance, there seem to be some moves towards cracking monolithic systems into pieces for reasons of development agility. ACA limiting admin costs is a huge driver, as companies rightly identified lack of technical agility as a existential threat (no agility = no ability to update automated processing pipelines to changing requirements = manual processing = penalties for exceeding allowed admin costs).
Also, I think there's a generational shift at the executive level from "Buy and trust vendor" to "Own, develop, and operate."