An Incursion with a universe that had no Earth wouldn’t have been a problem, since Earth was the centerpoint of the Incursions–the other universe’s Earth would have passed through empty space, and both universes would have survived.
I can’t help wondering if Hickman might answer this differently.
The incursions are a result of Molecule Man and Doom tinkering with the fact that Molecule Man exists as a single pan-universal entity. We have reason to hypothesise the incursions are actually focused on Molecule Man.
This would imply that where Earth didn’t exist Molecule Man would be a denizen of another planet that became the incursion point. It just so happens that Earth exists in a major fraction of all universes and the story was obviously focused on Earth.
