Entitled The Cole Protocol the next novel is going to be penned by Tobias S. Buckell, an up and coming sci-fi writer, and is going to deal with a supposedly new perspective and the Spartan Gray team. So far the only mention of other Spartans (warned ya 'bout the nerdiness) in the books are a few passing references. There was this from Ghosts of Onyx: "And what had ever happened to Gray Team on a mission far outside the confines of UNSC space, now missing for over a year?" and then this from Fall of Reach: "Assembled here tonight, are all surviving Spartans save three, who are otherwise engaged on fields of combat too distant to be easily recalled."
The book is set for a fall release and more about it should be revealed as the final date inches ever closer. You are all now that much closer to being Halo otaku. Glad we could help. (Also, to avoid any confusion, that cover isn't real, it's a 'shop.)