In the version of Back to the Future released in our timeline, Michael J. Fox plays Marty McFly, who goes back in time and inadvertently prevents his parents from getting together. Ouch!
However, according to Gizmodo, Ben Nevidi has seriously changed his mind about releasing For All Mankind. In that world, McFly would have been played by Eric Stoltz, not Fox. This is a particularly clever twist, since Stolz is actually was original Marty. After five weeks of filming, Stoltz was shamefully replaced by Fox at the behest of the producers, and the rest is history.
Unfortunately, the For All Mankind team was denied permission for this joke due to legal issues. It’s a shame because this gag would have worked great in “For All Mankind” but it’s also not that surprising. For many years, those in power were very protective of the whole episode with Stolz, as if no one wanted to hurt his feelings. However, even though we don’t actually see it, we can imagine what would happen if the Russians got ahead of us on the moon. At the very least, it would probably be great for Eric Stoltz. Or maybe not. That’s the beauty of a show like For All Mankind.