SCSS has better tooling, including better Stylelint support (which would be really helpful in taming all the CSS we have). It's also more extensible, and has some exciting plugins (like chroma.js support, and support for advanced colour spaces). Functionally speaking, I don't know of anything we'd lose if we made the switch.

This is also a good opportunity to migrate the pre-processor to PostCSS's SASS plugin, so that all CSS transforms are being managed in one place and we have finer control over what order they fire in.

• run script to migrate *.less files: https://github.com/debba/less2scss
• finish cleanup of script results
• finish migrating *.vue files
• set up basic stylelint configuration
• lint everything (where practical)
• enforce style conventions