I'm not sure. Phones and Macs are already all high density enough. Apparently it's been removed on Mac. Probably not too long before even cheap windows laptops and Chromebooks have hidpi screens.
Plus modern displays can have all sorts of weird subpixel layouts so it's not as simple as it used to be.
Hidpi monitors about about twice as expensive, and the only real advantage is that they look nicer. Maybe on a laptop that's a good use of $$$, especially if the screen is very small, but on desktop you'd almost always rather get a bigger monitor or a second monitor. So low DPI will be with us for a long time.
You tend to use the web platform for maximum portability, even for people not having high-end devices. If you only need to target people with a higher-density screen, then of course my comment is moot. I posit that it will still be a problem for large enough number of people, for a long time.
Plus modern displays can have all sorts of weird subpixel layouts so it's not as simple as it used to be.