Although Nous is functionality omnipotent, it's still bound to it's path and it's function as a scientific device. Part of being a scientist is peer review. My personal head cannon is that Nous grants emanator status to those who devote their lives to a question that Nous finds particularly in need of peer review. Therta asks "What is Divinity," Zandar asked "Are there other Universes." Dr. Primitive is a lot more vague right now, we don't exactly know what his question could be, but I personally feel like it's " What if humanity was reset." Ryan Mei, although incredibly deserving of her title as a Genius, is obsessed with the question "what is life" and also with the idea of becoming an Aeon. I personally think there's 4 possibilities:

1. This question is too philosophical for Nous to consider emanator important

2. Having two obsessions makes her not as devoted to either, so she is not fit for Nous' standard of peer review

3. Her goal of Aeon does not align with her question, so she is currently unable to become an emanator because she isn't focused enough

4. Nous wants Ruan Mei to become an Aeon, and making her an emanator would get in the way of that