If you think the heavy work is solely in the back-end, I'd encourage you to go ahead and try to build and release a front-end. We would happily use yours if it were good. We built the Ottehr front-end after building "the proprietary service" and realizing just how difficult it was to actually release an EHR without a front-end reference. You are also welcome to point Ottehr at some other back-end service if you want. Our goal is to encourage a new generation of EHRs that better support interoperability.