A data structure server is a nice and lofty goal for that I think. It has networking, command/protocol parsing, async operation, nice data-structure work so fairly well rounded project.
I don't think everyone was naysayer about your submission. Some including me were confused about the purpose since it reflects how we should look at it. If it was done to explore redis like server but with different priorities/knob everyone would have wanted to explore if that helps their use cases or how that affect the tool. Since its for learning the focus might be how readable/understandable the code is and maybe trying to learn from it themselves.
I hope you learn the kind of things you were planning to.