> To stay relevant, Pico CSS would need a full rewrite: plain modern CSS instead of Sass, built on features it doesn't use today (OKLCH colors, cascade layers, Popover, anchor positioning) with fallbacks for older browsers, and a native compiler that strips unused CSS and makes customization easy.

Does anyone know a similar project doing this?

We do: https://github.com/anyblades/blades

Already plain modern CSS instead of Sass, has Popover API, and CSS layers for individual components, OKLCH colors are on the way.

Drop-in compatible with Pico CSS (via underlying fork)

But why? Is it not relevant anymore? It's as useful and capable as it was years ago