Reading that thread, does say very clearly that he doesn't know how this affects where the ota comes from and that for all he knows ota will work as usual.
If I read correctly, he's saying that aosp will not support region specific features. Makes sense. The Japanese GN for example includes the earthquake early warning app, and maybe that requires some framework or some other changes? I don't know but just throwing that out there. It makes sense that such changes would not be in aosp and thus couldn't be built by cm or other people in custom roms.
From there it's easy to assume it means google can't push out an ota...but nobody knows for sure yet.