Using the hash for navigation is still quite common, because usage of history pushState requires server support to correctly work on reload.
I’d also argue that SPAs using it for navigation are not abusing it. The purpose is to allow linking to different sections in a document. Navigation is effectively an advanced form of the same concept. It’s just that as you navigate, the DOM happens to mutate to bring the content you linked to into view, instead of just scrolling down to it.
Hash fragments are for page authors to define, not the browser. While this sounds like a useful feature, it’s implementation is simply wrong.
What they really want to do is extend the RFC for URLs to add an additional component. There are already unsafe characters that could be used for this purpose that would be nonbreaking.
For example, add a | at the end of the hash fragment, and anything after that can be for the browser to communicate page state independent of the page author’s intent.
The current proposal, however, should be firmly rejected.