This has been bouncing around fandom for a few days, but here it is, officially: The Art of Star Wars Rebels is coming out in October. The hardcover is written by Dan Wallace and “will chronicle the making of the show over its four-season run, complete with never-before-seen concept art and process pieces.” It will include commentary from Dave Filoni, Simon Kinberg, Carrie Beck and others, and is already up for preorder.
For the time being, there’s plenty of behind the scenes content in the series guide on StarWars.com, including the above, a lighting concept by Molly Denmark for the series finale.