Not sure if this is possible in the webkit view you use, but I’d love it if we could toggle Reader mode for Web pages that we have imported into Scrivener. Opening the webarchive in Safari and I can switch into that view but I’d rather do it directly in Scrivener!
I don’t believe that’s a web kit feature, just something added on top by Safari. Maybe if you don’t want the stuff around the article in the first place, just archive the article text instead of storing all of the ads, navigation banners and tons (and tons, and tons these days) of Javascript and other vectors for instability. An easy way is to use the readability plug-in in your browser of choice, then print as PDF to Scrivener. Or the method I use it to import pages and convert to text, then strip out everything I don’t want, right in Scrivener.