Hello,
Nuendo 6.5 is going to be released in beginning of Q2 2014. Beside all features already revealed in Cubase 7.5 it will get even more post-pro / surround mixing relevant functions, such as a professional Bass Management. In terms of development time, it simply takes longer to bring all the additional features into the upcoming Nuendo 6.5.
We may also be able to correct some more issues in terms of GUI, but in general it will be the status of Cubase 7.5.
Key Command/mixer issue will (most likely) be fixed.
Thanks,
Timo