They discuss some aspects of his new project here (please note that the interview contains some minor spoilers).

(Source: via @EUCantina)

(Source: Celebration V Exhibitor Exclusives list [PDF] via TheForce.net)

Knight Errant is a new comic and novel series set 1,000 years before The Phantom Menace and features the story of Jedi Knight Kerra Holt as she struggles to cope in Sith controlled territory. Both comic and novels will be written by John Jackson Miller, author of Knights of the Old Republic comic series and Lost Tribe of the Sith e-book series. It begins in October with the release of the first issue of a 5-part comic series Knight Errant: Aflame, while the first novel is due for release in paperback in the US on 25th January 2011.

UPDATE: StarWars.com has posted a better image of the novel's cover as well as the first synopsis:
WARNING CONTAINS POSSIBLE SPOILERS Highlight between arrowheads to read>>>The Republic is in crisis, torn by plague and conflict. The Sith roam unchecked, vying with one another to dominate the galaxy. But one lone Jedi, Kerra Holt, is determined to take down the Dark Lords -- one act of sabotage at a time. Her enemies are strange and many: Lord Daiman, who imagines himself the creator of the universe; Lord Odion, who intends to be its destroyer; the curious siblings Quillan and Dromika; the enigmatic Arkadia. So many warring Sith weaving a patchwork of brutality -- with only Kerra Holt to defend the innocents caught underfoot. Sensing a sinister pattern in the chaos, Kerra embarks on a journey that will take her to many worlds and into fierce battles against even fiercer enemies. With one against so many, her only chance of success lies with forging alliances among those who serve her enemies -- including a mysterious Sith spy and a clever mercenary general. But will they be her adversaries or her salvation?<<<

Dark Horse Announces All-New Star Wars Series, Knight Errant!
AS KNIGHTS OF THE OLD REPUBLIC DRAWS TO A CLOSE, WRITER JOHN JACKSON MILLER MOVES TO AN UNCHARTED CORNER OF THE GALAXY!

Coming off the heels of penning the breakout hit Mass Effect: Redemption and the gripping finale of Knights of the Old Republic, writer John Jackson Miller introduces us to Kerra Holt, a young Jedi who’s about to realize that her role in the galaxy is far more important, and vastly different, than she could have ever imagined.
Set one thousand years before Episode I, in a time referred to as the “Dark Age of the Republic,” this story takes place in an era when the Sith were legion and the Republic was strained to the breaking point, leaving large swaths of the galaxy with no one to turn to. This pivotal time in the history of Star Wars has been largely unexplored, until now.
Additionally, for the first time ever, the writer of this new comics series will also be authoring a novel for Del Rey Books, set in the same era and involving the same cast of characters in an all-new adventure. It’s going to be a unique event for Star Wars, and one that will give fans a whole new perspective on the galaxy.
“There’s such wonderful chaos going on in the galaxy in this period,” said writer John Jackson Miller. “More than a generation before Darth Bane introduced the Rule of Two, Sith Lords are colliding not just with the Republic, but with each other. Kerra’s going to find that good intentions just may not be enough in a galaxy gone mad! This is a wide-open area to explore, and I’m thrilled that Dark Horse and Del Rey have given me this opportunity to do so.”
“With John writing both the comics and the novel, Knight Errant will be a Star Wars story on a scale we've never undertaken before," said comic-series editor Dave Marshall. “This will be a first-of-its-kind opportunity to introduce the Expanded Universe of the Dark Horse comics to the fans of the Del Rey novels and vice versa!”
With more news in the coming months, look for Star Wars: Knight Errant to arrive on shelves later this fall!

(Source: Dark Horse Comics)