I have several use cases where I want to import a css file from another app, or a dependency app, or even within the app itself (changing the theme mid-app depending on the form). I want the color references in those css files to work.
My main use case is importing the theme, with all the colors, from a dependency app into my main app (EDIT: this is now solved with an update that came with the Layouts feature).
I figured out how to do this with a workaround described in the post linked above. However, it requires a lot of changes to my theme.css (breaking up the theme.css into two css files - one for variables and the other for the rest).