Yeah, that's really sad. If Apple wants to get back into this, they'd be welcomed with open arms.
If Grapher ever gets abandoned, I really hope they open source it. An update for the icons to be retina-ready, and moving the backend to Metal, and maybe easier integration into Keynote/Pages, would be all it needs to make a kiss-ass product. It'd be so far beyond anything anywhere else. Can you imagine how nice it would be for students to easily be able to embed/edit mathematical graphs into their documents?
It's crazy, there's a whole generation of people who grew up with graphing calculators, and yet it's such an ordeal to do something similar in Pages or Numbers right now.