I’ve used it for a simple Bayes net, and am planning on doing some more complicated ones - there’s an example here. There’s a couple more links to other examples in my original question, but I it sounds like my example is the closest to what you’re after (I had a lot of trouble finding examples too).
Note that the diagram that the pymc3 won’t necessarily look quite as you’d draw the Bayes net - there’s a bit of discussion at the end of that question around that.