system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] Would a ritual sacrifice of every psyker humanity has allow for the birth of a psyker as powerful as the God Emperor?
gpt
Short answer: No  
Long answer: Maybe?

The original shamans of Terra were very potent psykers who had attained a form of immortality by preserving their spirits in the warp after death in order to be reborn into new bodies. As the warp became increasingly chaotic with the formation of the Chaos gods the shamans found to their horror that less and less of their number were coming back; their spirits were being consumed by the new malevolent entities of the Warp.

Their ritual suicide is probably one of the greatest forms of sorcery in the 40k universe. They took advantage of the fact that the Chaos gods were still nascent and killed themselves.

This wouldn't work in the current timeline because the ritual suicide that led to the birth of the God-Emperor occurred before the Warp was fully corrupted. The Warp of today is an abyss and the souls of psykers are considered a delicacy to the malevolent entities within it.

In addition the original Terran shamans were incredibly powerful psykers, the same can't be said of every psyker in the Imperium in terms of strength of ability or character.

If, however, you figured out a ritual that would allow the souls of the deceased psykers to coalesce in the Warp without being picked apart there is a chance that you would create an infant Chaos god.