They already include test frameworks.
It would be cool to have, at least as an experiment, a language with no snowflake horrors at all, if it runs at all, it's in the language or framework's One True Way All Tools Understand. Static typing, maybe even linter warnings as fatal errors, anything that makes adding CI a hassle just doesn't exist.
Maybe it could even refuse to run without full test coverage.
So you could take any project at all, click "Turn on CI" and that's that, there's only one CI config that exists.
I'm guessing the number of use cases would be tiny to nonexistant in the startup centric tech world, but they might be some of the least stressful projects ever made!