In reply to Pete.
“Editors are for content not presentation. Adding columns is a presentational feature. To do so breaks wordpress as a cms.”

Agreed. However, IMO most front end builders I’ve seen have already kowtowed to the users that wanted the editor and builder to exist in the same space despite any misgivings they may have had. It would not seem that people care anymore.

Those who have used or made builders like this have already violated this paradigm. So, at the very least the WordPress.org dev team wouldn’t be the first to do so.

Backend builders are often better at keeping things separate but these users don’t like them. That’s not to say that there are not those who don’t still prefer to do editing on the backend. I’m one of them.