Looking through the tag, the status of the e-book was last brought up in 2015, and Monica Cellio, one of our moderators at the time, had this to say on the subject:
My guess is that nobody has been sufficiently motivated to move it from "idea" to "first stages of an actual plan". Anybody who'd like to work on that (or any other) project should feel free to step up!
...and evidently, nobody did.
It's a shame, but it does seem as though nothing more came of this project since its initial announcement back in 2012. I wouldn't say it's been cancelled or dismissed, more like... forgotten about. Especially since most of the people involved in its creation left the site following Monica's dismissal.
This is the first I'm hearing about this project, but I'll echo Monica: this could be a great idea, and if anyone wants to pick it back up again, I'm sure the original creators won't mind. But... realistically, this probably isn't going to happen.