When Yosemite was released Apple also released an update for iBooks Author. The bug with opening documents made in previous versions of OSX has been squashed. Authors hoping to edit and update older multi touch iBooks can continue to do so.
iBA is still awaiting an update to its UI to bring it inline with the iWork apps. But a functioning app is of far greater value than a beautiful and useless app.
Hope you authors are happy with that result! But maybe you were banking on a delay between the releases of Yosemite and the iBA update so you could have a holiday?