Just wanted to give everyone a heads up. udev interface renaming (via /etc/udev/rules.d/70-persistent-net.rules) worked flawlessly in Buster, but seems broken in Bullseye. Don't know if this is an inherent udev bug or whether another package is impacting udev (maybe systemd?). At any rate if you examine /var/log/messages you'll see that no renaming takes place as the kernel boots. Debian bug report has been filed.
UPDATE: Apparently this is intentional in Bullseye as described in https://wiki.debian.org/NetworkInterfaceNames. However as per this wiki it still ought to be possible to regain the old renaming. I have not been successful with any of the techniques described so we'll see how my Debian bug report is responded to.