Is further simplification planned here?
From a theme development perspective getting full control over the colours used in Discourse is still quite painful. To take the tertiary colour as an example, there’s still 30 instances of scale-color($tertiary, $lightness: N%).
I’d rather not override every one of those in my custom CSS, and my mad science experiment 
overriding the scale-color function to output only a limited, palette defined, set of colours didn’t work.
The best situation from my end would be a complete replacement of the use of scale-color with, for example, $tertiary, $tertiary-low, $tertiary-very-low, etc. alongside the ability to override those variables from a theme.