Related to #3, the doiuse library warns about using CSS properties which aren't supported in a given set of target browsers backed by caniuse data (vs stylelint which focuses more on general CSS mistakes). This could be useful to warn not only about adoption of newer features, but also older features which haven't been implemented in all browsers (e.g. the CSS zoom property). There's even a stylelint plugin that wraps this, but I suspect it'd be better to avoid the extra middle man.
Originally reported by @antross in https://github.com/webhintio/hint/issues/1203