Is JEDI only meant to interface with FV3?

No, JEDI is designed to be easily adaptable across an unlimited range of models that we expect will extend beyond numerical weather prediction. Currently we have about 11 atmospheric and ocean models that are interfaced. JEDI-FV3 is merely the first release of JEDI (initial release October, 2020). We have plans to release a second model application, JEDI-MPAS, in September, 2021.