We can't even say for sure when TSLRCM 1.8 will come out, let alone M4-78EP
I won't try to guess or estimate when M4-78 will be ready for release. We just got a new "build" ready for testing, and none of testers started playing it yet as far as I know; after everyone play test this one, there will be another one, with bug fixes and more content (that means more side quests... mostly). Then probably another one, and as many builds as necessary to make it as polished as possible for release...
Then there is also VO recording, which could also take a while.
So overall, we can't answer any questions about the release date. That's impossible to predict.