Thanks for reaching out! For various reasons, I left the team and actually don't work on TensorFlow Probability anymore (including the Edward2 as-is in that repository). So I may not be the best person to help diagnose the user question.
With that said, one helpful reference could be Danijar's code (
https://github.com/brain-research/ncp). It uses an extension of TensorFlow Keras layers to implement variational BNNs, and the toy figures do indeed show high variance outside the distribution of the data inputs. But it depends on the model—variational BNNs don't guarantee it. Software-related, one of our plans is to redesign the layers to something we can iterate a bit more easily with, both in that code base and in other Bayesian neural net work. Hopefully that might also be useful for whatever you're using BNNs for!