Having worked on _s since its birth, I think "starter themes" or "frameworks" or whatever you want to call them aren't a great idea unless you're prepared to maintain them, nurture active discussions around them, and also keep them updated.

I also do not believe that a one-size-fits-all parent theme will ever exist because themers push boundaries and are incredible designers - new becomes old quickly. As far as a component library on the front end goes, sure, but a ton of those exist already.

Best practices and standards are a moving goal post and every year default themes push those forward. Disparity between all default themes, a "master" theme, other starter themes on the market, and innovators who like to push boundaries will continue to happen to a degree.

I also believe that headless approaches to site building, where people can do whatever they want in something like Gatsby, on their own terms, while pulling in content from WordPress will become more popular. I've certainly found myself enjoying building headless themes and sites lately with a WordPress-as-content only approach.

If given the choice between developing with a master WordPress theme (or set of components that a group of devs will create) or spinning my own stack up that I'm comfortable with, I'd probably go with the latter.

I do think that theme developers have been a ridiculously undervalued asset in the WordPress ecosystem since long before premium themes, frameworks, starter themes, and Gutenberg existed. It wouldn't shock me if they continue to be pushed aside for the betterment of non-theme Core, even if that means ending up with CSS classes that read like college essays.