Plotting priors in traceplot

Questions
2

Yeah I dont think many ppl is using it, as it gets quite confusing with multi-chain and/or multivariate RVs. It is great for demonstration purpose in low dimension toy problems, a use case is something like this:

with pm.Model() as m:
    mu = pm.Normal('mu', 0, 1)
    sd = pm.HalfCauchy('sd', 1.5)
    obs = pm.Normal('obs', mu, sd, observed=np.random.randn(10)*2.5+1)
    trace = pm.sample()

pm.traceplot(trace, 
             combined=True,
             priors=[pm.Normal.dist(0., 1), pm.HalfCauchy.dist(2.5)]);

# this is also allow
pm.traceplot(trace, 
             combined=True,
             priors=[mu.distribution, sd.distribution]);

So yes I think what you are doing is correct at least in univariate cases.