"WordPress needs a solid front-end design framework."

In theory, maybe. The reality is, Gutenberg (for example) is so fraught with inconsistencies, quirks and whatnots, that the idea of the same process (and similar team members?) doing the same for the front-end - for 30%+ of the internet?!?!? - is an extremely difficult elephant to get your head wrapped around.

Perhaps it would be better for WP to adopt an already proven and established framework and design system? What's better about going this route is it doesn't have to happen top-down. Theme studios such as yourself can form a "pact" and then pick your defacto standard. Others will follow; as following is what most of the WP community does best ;)