Another very interesting crossover, including both options of the Emperor being Kal-El, or knowing Superman in a distant past.Especially that Primarch's themselves, seem to be shout-out to Superman, being superhumans sent in capsules to distant worlds, from older, advanced (and also "fallen"/"destroyed", if in a far less complete way) world (Terra, like Krypton), were they brought up, ending up each as heroes, leaders and/or champions of some sort (even if some darker, like Angron and Konrad Curze.). Especially curious is that Superman originally was a human, but from a distant future (and his powers being a result of evolution over ages), sent in past right before Earth meets it's end, hence his nickname "Man of Tomorrow".(First a an adult adventurer-scientist a, who gone to past, in the second version is a son of a scientist who sent him into the past before the planet exploded.):This was ultimately used in the (original comic version of) Superman: Red Son.