Did you miss the "YC W17" in the title? Of course they're announcing their launch on news.ycombinator.com. (Mind you, they probably rolled their eyes as they hit submit, knowing they'd get this kind of comment.)
Not have to! Just can if they want to. Let me dig up the links for you where I posted about this...
Edit: here's the rundown so far: https://hn.algolia.com/?sort=byDate&prefix&page=0&dateRange=.... Those comments trace the history of how the idea is evolving. I like explaining it to the community this way because the minute we announce something formal, people forget that it's all experimental and subject to change. But once it stabilizes we'll add it to the FAQ or something.