Great tool! I have some ideas for improvement, as you have stated you are open to that.
OSMNX will allow for a custom filter, so you could use a filter that matches exactly the filter used at Citystrides, that would be a nice touch and keep from trying to route us onto roads inappropriate for running.
Docs: https://osmnx.readthedocs.io/en/stable/osmnx.html?highlight=custom%20filter#osmnx.graph.graph_from_polygon
It appears the details of that query can be found here: Overpass Street Query
It would also be great if the starting node for the Eulerian circuit could be specified. So that one could aim to start at a good parking location for instance.