The JS API for interacting with Sass, which is now shared between Dart Sass and Node Sass, is in need of an overhaul. The current APIs are showing their age: they make it difficult to write plugins that behave similarly to native Sass features, and they're hard for Dart Sass to implement efficiently.
This project is tracking the design work that needs to be done to figure out what these new APIs should look like. Once that's in place, it will also track meta-issues for implementing the APIs across both Node Sass and Dart Sass.
Note that this is only tracking issues in the sass/sass repo. Individual implementation's issues will be linked from the issues tracked in this project.