I've just stumbled upon an old article with some speculative renders of a possible E89.
An artist's impression or not, it could've been a looker.
I even prefer it to the Zagato effort - it manages to reconcile the best of the E86 and the E89 while still looking like a bimmer.
http://www.bmwblog.com/2010/08/10/rendering-bmw-z4-coupe-based-on-e89-roadster/
And the Italian rendition:

An artist's impression or not, it could've been a looker.
I even prefer it to the Zagato effort - it manages to reconcile the best of the E86 and the E89 while still looking like a bimmer.
http://www.bmwblog.com/2010/08/10/rendering-bmw-z4-coupe-based-on-e89-roadster/
And the Italian rendition:
