I wonder though if this is a theoretical vs real world problem. I get the desire for fidelity, but would prefer to hear about a few specific cases where this is causing an issue.
The trouble with introducing a setting like this would be re-applying normalization rules when you fiddle with the allowlist of sites, it would make it a very complex change.
We now normalize unconditionally (regardless of the site setting) so turning it on is instant and applies to all history.
Awesome 
All thanks to @nbianca