Take Musu Aiki
No details as to time frame, but I have heard from a reliable source that a translation of "Take Musu Aiki" into English is in progress.
"Take Musu Aiki" is a series of lectures by Morihei Ueshiba transcribed by Hideo Takahashi for publication in the Byakko Shinko Kai newsletter. It is the largest (and only, really) collection of Morihei Ueshiba's thoughts on the philosophical/spiritual side of Aikido.
It's available in Japanese from the Byakko Shinko Kai press.