Really cool talk Dan. I had no idea PyMC3 was so popular in astrophysics.
I think your areas of improvement are spot on. Regarding the second point, do you want to write that into a github issue?
Also, did you find our announcement here: https://pymc-devs.medium.com/the-future-of-pymc3-or-theano-is-dead-long-live-theano-d8005f8a0e9b clear up the confusion as to your point #3?