UW Technics has announced their external TTL controller for Nikon. Compatible will all Nikon cameras and available with optical or electronic output, it is attached via any M14 housing port. It is compatible with Z-240, YS-250, DS-161, YS-D1, YS-D2 and strobes.

From UW Technics Facebook page

UW TECHNICS External TTL-Converter. Compatible with all Nikon cameras, including newest D500 and D5. Universal M14 screw mount. Variants with optical output connector or electric (N-5, S-6, Ikelite) connector. Available versions for Z-240, YS-250, DS-161, YS-D1, YS-D2 strobes.

Please email UW Technics for more details.