Once LibreSSL has reached a point of minimal disruptive change, FIPS support could be re-implemented as a series of third-party patches, which could then be certified as needed.
For example, create a fipssl project which is patches to a specific version of LibreSSL; take the result (LibreSSL v1.x + fipssl v1.2 = libfipssl v1.2) and then get that certified. Companies/contractors which need FIPS certification then use libfipssl v1.2.
The fipssl maintainers then just have to track LibreSSL changes until their next release, which (for a series of small, maintainable patches) shouldn't be too difficult. The grsecurity project has been doing the same thing with the Linux kernel for years.
For example, create a fipssl project which is patches to a specific version of LibreSSL; take the result (LibreSSL v1.x + fipssl v1.2 = libfipssl v1.2) and then get that certified. Companies/contractors which need FIPS certification then use libfipssl v1.2.
The fipssl maintainers then just have to track LibreSSL changes until their next release, which (for a series of small, maintainable patches) shouldn't be too difficult. The grsecurity project has been doing the same thing with the Linux kernel for years.