Is that paywall busting even an actual goal/requirement in reader mode, or just a fortuitous side effect of the way it does its "web clipping" (is that still a term?)
It's an intended side effect. The paywall banners are also just clutter to remove from the DOM, often the entire text is still there.
Technically, messing with paywalls is forbidden for Chrome extensions listed in the webstore (and detrimental for getting press coverage). Which is why no one advertises this.
