Has it actually been started?

As StJohn said, it's been started. Public posts and comments are available, but not much else.

What percentage is complete?

Maybe 20%? Right now, the big thing missing is the ability to log in to see private data. Once that's added, we can add endpoints one at a time. And we can certainly take requests for what to add first. The end goal being, to be able to get any data that you can get from a webpage right now, via the API.

Where on the priority list is it?

Hubski is a team of several people, each working on their own projects. The API is mine, along with spearheading the conversion from Arc to Racket, and converting to SQL, both of which are related. It's at the top of my priority list.

Unfortunately (for Hubski), my life became a lot busier last Fall. I started a new job, and taiji lessons, among other things. Right now, the weekends are the only time I really have, and then about half my weekends end up being busy.

TLDR I'm working on the API, I have much less time than I used to, but it's getting there. I'm about 80% done with adding API auth for private data, and then it's just one endpoint at a time.

Is there an estimated date of arrival?

Not really, sorry. I'd optimistically hope to have API logins around May, and a dozen or so endpoints by June or July.

I'm only interested in real answers

The API will definitely be finished by the first of Octember.