...If you were Captain Ret-Con for a day and had the power to retroactively configure or add something significant to the lore, what would it be? Would you advance the Tau deep into the Third Sphere Expansion, giving them a psychic client race to afford true warp travel?

Would you set Necrons back to being soulless drones in the service of Cthulhu?

Would you revive Squats?

Would you make the Emperor slowly recover, glutted on the regenerative souls of ten thousand years of psyker tribute, blinking away the dust from his eyes and looking over his own ruined, whithered body... only to ask the Custodes in a sound like granite dragged over sand...

"My sons... Where are my sons?"

This isn't so much about how you'd like the 40k universe to turn out, however. Rather, it's a question of what you genuinely think would make it -better- as a setting. Surely, everyone has an opinion on that.