The most significant feature of PostCSS 8.0 will be a visitor API for plugins. PostCSS is the parser, which parses the CSS to an object tree (AST). Then plugins change this tree. In the end, PostCSS generates a new CSS string from a modified object tree.
Currently, every PostCSS plugin walks through this tree. Often a plugin is looking just for a few properties, but it still needs to scan the whole tree. If you have many plugins in your build tool (or you use one plugin preset with many plugins inside, likeAn excerpt from PostCSS 8.0 is coming
stylelint), most of the processing time will be spent in plugins walking through the tree again and again.