Appreciate the thought behind using the hashed URL to avoid leaking PII. That does make comments difficult too though because of refs being inserted by various social platforms. Not sure how one would handle that though
Some sites use a link with real=canonical to indicate the canonical url. Maybe this could use that (when present), instead of the tab url?
Comments can be seen like this:
https://comntr.github.io#http://contoso.com/
The trick is that the #... part of the URL isn't sent to the server. This request downloads JS which computes SHA1 and gets comments by that hash from the data server.