James Shigeta was going to play Nogura if the Phase II series had progressed.
Where did you hear this? I know Shigeta played Nogura in a fan film called Yorktown II
back in the late '80s or so; Starlog
covered it, since it was apparently a pretty prominent fan film with involvement from many professionals including George Takei (with the filmmaker playing Sulu's son), Andrew Probert (who designed a Klingon scout ship for it), and composer Bill Conti. But I don't remember anything about Shigeta being slated for Phase II
For the life of me, I can't recall where I read this, but I'm certain I did. I want to say that most likely it was in the Reeves-Stevens' book on Phase II, but I'd have to flip through my copy to see if I can confirm that.
What's really a shame is that Mifune wasn't able to play him in TMP.