Without going and digging around for it, I am almost sure I read or heard an interview with Wyatt where he said the Magic settings he had done as free pdfs were not likely to get the hardcover book treatment, or they would be at the end of the list behind all the other settings, or something like that.
On a side note, if they ever do a hardcover adventure for Ravnica, I hope it is based on this:
Magnificent hardcover art books featuring the incredible images and lore of Magic: The Gathering®!Danger and adventure await in these pages, lavishly...www.simonandschuster.com
There's also the Rabiah Scale. The top five settings are Dominaria, Ravnica, Innistrad, Zendikar, and Theros. We're 2-for-2 so far, and I would expect that we'll probably see at least one or two of the others, although all three have received Planeshift PDFs.