This question is currently closed for being off-topic. I am not the author of the question, but I find the idea very interesting.
It asks how to design a coed school that feels realistic. I believe "realistic" in this sense is the same as a "realistic" fictional tech. This site has allowed fictional science/tech that is just near enough with real life science/tech. As it stands, the question comes across to me as asking for some fictional sociology (or other social-science or psychology backed reasons) that can allow a setting to occur.
This bit here surely makes the question sounds like asking to solve a real-world, present-day problem:
mainly for plot/world building reasons, but also because I think it is an interesting concept to see how this could realistically work if implemented, either now or in the near future.
However, I see it as the social equivalent of "how can I make this available using near-future tech".
But apart from that -- and most of OP's other arguments that sound like they're trying to make this happen in real-world -- is the question really off-topic? If so, what can one do to make it more on-topic?
Or does the question assumes too much of modern-day Western human culture that it can't be made on-topic one way or another?