100% - and the catch is that IMO the one backend would need to be built first, and deployed in a nationally-coordinated fashion across the continuum of care. Otherwise, the first-mover disadvantage would be prohibitive for any one IDN, clinical lab, etc. to both build and maintain the internal capabilities they need, while simultaneously building and maintaining interoperability with everyone else still using proprietary solutions.
Since steps in this direction feel like they’d need to come from regulatory bodies, I suspect that things like this - Let's prepare at POC: "EU OS" KDE Plasma workstation for the EU public administration - would be helpful proof points in getting folks with those agencies to “believe in” top-to-bottom FOSS stacks.