Tachyons is feature complete for most people's/project's needs. It doesn't need to be updated. Every day we all use code that was last updated 10+ years ago without realising it.

Having said that we switched to Tailwind for a very specific reason: customisability. see: https://github.com/dwyl/learn-tailwind#what-about-tachyons

Still Tachyons is a perfectly valid and lightweight utility class based CSS library.