Federico Viticci does a great job pointing to all of the resources regarding the Apple News format, including documentation and API details.
Initial Charge has been available in Apple News since the launch of iOS 9 in September, but Apple had not yet made the tools available to the public for publishing specifically in the Apple News format. Aside from a few publications hand-picked by Apple, everything has been fed into the service by RSS (which has been less than perfect, to put it lightly).
I’m not sure if I’ll actually be publishing anything in the Apple News format in the future. But at the very least, I plan on digging though the documentation to see how it works and to gauge how long it might take to build it into my workflows — even if only for a select few feature articles.