How do you envision this working technically? So, you write a post, then submit it, and instead of the post being baked based on the site settings as before, your individual preferences are now checked. I can still understand that.
But if I quote your post in my post, then your preferences would have to be applied to the quote, and my preferences to my part of it. That’s where it gets tricky, in my view.
The same goes for when we both edit the same wiki post one after the other.
I also see a problem if posts need to be re-baked later on. For one thing, it’s more likely that users will change their preferences than that admins will change settings without being aware of the consequences, so old posts might have been written with different preferences. Plus, the author and their preferences would have to be checked for every single post.