I think ^? is the default for Backspace in iTerm2. Although it has an option to send `^H`, it is disabled by default and discouraged to enable as it will change some other existing keybindings.
It did not change recently, no, and I doubt it has changed on Terminal with the upgrade to macOS Catalina.
Many thanks for the quick response! I'm looking forward to the release.
Also, for the bug, do I understand correctly that it will only work with `nano -K` ? If so, does that mean mouse support will be disabled ? (not that I've never used mouse in nano, I have just discovered the possibility when testing -K for the bug (: ).