I may make a pull request if I can ever find the time to set up for it and familiarize myself with the LXML infrastructure. (I found them while I was already building a custom allow_tags for lxml.html.clean.Cleaner, so correcting it in my code is trivial and my time is limited.)
Also, I should probably mention that <bdi> is a very important tag since it's basically the HTML's way of sandboxing against unpaired Unicode LTR/RTL text-directionality control codes.
I take pull requests.