Oh, I see. I had mistakenly guessed that the thing in the menu containing other privacy protection settings (ITP, content blockers, cookies) was also about privacy. I should have indexed more heavily on the reader mode outlier.
If third-party font blocking were something to be included, perhaps it would look something like this
and in the preferences menu for font blocking turn On/Off into On/Third-Party/Off. The backend changes to check the origin are probably more involved. I'd take a whack at it myself if I could build my own Orion.
I don't think that it's as important to offer the option for JS since it's trivial to send data to third parties using it, and to my knowledge third-party cookies are already disallowed by default and not much good can come of them anyway.
On the other hand, the same could be done by disabling the browser's content blockers in favor of uBlock plus a fonts rule. However, it'd be cool to more universally defeat google's font tracking by making the option easier for users to set.