I think this ship, if it hasn't sailed already, is at least starting its engines and getting ready to leave the harbour.
User agents and servers are increasingly trending towards an adversarial relationship, where the user doesn't want to do much of what the server is asking of it. This has been true from the first pop-up blockers, through to modern adblocking and anti-tracking measures (the situation now being so bad that tracking protection is a built-in default feature in some browsers).
Eventually, a "filter out the crap" strategy becomes too onerous, an "extract what looks good" strategy starts to look better, and you end up with tools like Reader Mode. Custom clients are a natural next step - when someone gets desperate enough to write an article-dl to match youtube-dl, we'll be there.