This is a big request: Improve "design in the browser" capabilities. i.e. pushing CSS/HTML and maybe JS changes made in Dev Tools back to the source files without manual shenanigans in the middle. I probably waste more time copying CSS / HTML tweak diffs from the browser back into the related source files than anything else with in browser dev tools. Due to the nature of 'losing changes' if I happen to hit refresh or…
It's not always possible to push changes back to LESS or SASS due to ambiguity at which level changes should be applied - if you're editing CSS values. The browser would have to display SASS or LESS in the inspector for what you're suggesting to work.
Now, if you have the "Support for Sass" experiment enabled, you'll see the "Auto-reload CSS upon Sass save" timeout setting to reload re-generated CSS files after "sass --watch in:out --sourcemap" (or equivalent) has updated them on the local disk.