Nothing's been signed yet, but Seventh Doctor Sylvester McCoy has been offered the role of Gandalf's fellow wizard Radagast the Brown in Peter Jackson's The Hobbit. If David Tennant gets in, we'll have a regular Whoverse invasion of Middle Earth.
McCoy confirmed his involvement to fans at the Armageddon Expo in Auckland, New Zealand. Radagast is only mentioned in The Hobbit (Gandalf refers to him as "his cousin"), so it's unclear how big McCoy's role will be in the film. Still, we hope that his incarnation of Radagast has at least a twinge of the Seventh Doctor's sartorial swagger.
[Via Gallifrey News Base. Thanks, Ursus-Veritas!]