Paris looked different 200 years ago. The most of rebuilt happened about 170 years ago. And people are in love with Montmartre which survived the rebuild ended up vastly older than the rest of the city. I’d even dare to say many people think of Montmartre style Paris rather than the rebuild.

Exemptions like you suggest would just open the gates for fancy corruption schemes. Here the public is okay-ish about historical buildings changes hands specifically because of strict rules.

A lot of public institutions are now moving from historical buildings to new buildings in outskirts because old buildings are expensive to maintain and not flexible enough for modern office working. And those historical buildings frequently get renovated (or, sometimes, reverted to) apartments. And the public is fine in general.

Excuse me if I’m wrong, but most of business activity is already not in SF. But people love living in SF for it’s charm. If you destroy the charm for the sake of lowering prices… why would people pick SF-proper instead of same boring buildings outside of the peninsula?