This state of play with FRDM-K64F is really quite unexpected.  Freescale and their new owners NXP are after all founding members of the Zephyr Project, and FRDM-K64F is not only their leading FRDM-series board but it is also the only NXP board which is explicitly listed as Supported.

Given the above, it would be very reasonable for any reader to assume that at least this one board would be excellently supported by Zephyr (as a result of NXP's support), especially in regard to its key features like built-in networking.  Evidently that would be a false assumption.

Do founding members of the project not offer to provide manpower support or running code, at least for their own boards?

I think it would be useful to understand the relationship between sponsoring corporations and the project better.  Despite operating under the umbrella of the Linux Foundation, code contributions in Zephyr may differ from the Linux model, for which companies commonly contribute kernel code for their hardware.

If this is written down somewhere already, a link would be awesome.  Thanks! :-)