I would hope (read: pray) that on HN a11y isn't jargon. On a thread about scrollbars (i.e., UI and UX) a11y should be as accessible as saying UI or UX.
Again, obscure and jargon are a function of context.
Spitballing...Keep in mind, without context, "accessibility" is also jargon in the sense not everyone is going to know what and how that means. My mum certainly wouldn't understand a11y, I agree. But she also would understand "accessibility" or even "website accessibility."
Full disclosure: I'm 5x more picky than the next person when it comes to comms. Absolutely, words matter. But one of the foundations to comms is context. The context in this case is HN.
