It seems like TheMightyCat just generates code, which cannot be upstreamed to pmOS due to the policy on generated code.
Their generated code has been criticised by some kernel developers because of lack of quality. I think some sensors were accessed without using hexagonrpcd, which means battery usage will be unnecessarily high, which is an improper way of doing it.
Also, mainline kernel support is actively being worked on by Fairphone employees, which know the hardware best. All remaining features will be added in due time.