Based on some of the recent interviews with Turley, I'd expect he'll be drawing heavily on the completed Joseph Smith Papers project for his biography. On one podcast I listened to with him, Turley's statement was that the problem with studying church history is that we don't study enough church history, and a little knowledge is a dangerous thing. While I agree that his volume will likely be a faith-promoting version of the life of the prophet, I also expect he'll deal with some of the controversies with documentation, from a believer's standpoint, at any rate.
My favorite biography of Joseph Smith has been Rough Stone Rolling, but one criticism I thought was interesting came from my father, who felt it too secular, or trying to explain Joseph to a secular audience. I found the analysis of doctrinal points fascinating, but perhaps there are those among the faithful who are looking for affirmation rather than explanation. Here's to hoping Turley can accomplish it; based on his books on Hoffman and the two MMM volumes, I'll look forward to it.