The WPT is the exact opposite of what I was talking about. The interesting thing about the Acid tests isn't their utility as a conformance test. Sure, that's what the were, but even at the time the problems with the tests were well known. The features they tested were incomplete and somewhat arbitrary. Most browsers didn't even bolter trying to get the last 3 points on Acid3, which tested SVG fonts. I'm sure WPT is far more useful from a technical perspective.

Unfortunately, WPT is missing the actual feature that made the Acid tests interesting: a design that could be used and understand by anyone. Most people are not going to go do the incredibly complex work required to actually run the WPT tests (which apparently involves its own command line utility to manage the process, requires knowledge of python/pip/virtualenv, and understanding platform-specific documentation for both setting up and running the tests.

For Acid2/Acid3, anybody could simply load the test URL to run the tests themselves, on their own browser and OS, and see the results first-hand. It doesn't matter that most people didn't know the various CSS/Javascript/etc features being tested. Seeing that your browser completely failed Acid3 was obvious[1]. It was exciting to see for yourself if the latest browser update scored higher on Acid3.

[1] https://en.wikipedia.org/wiki/File:Acid3ie8rc1.png