The thing for CUES that I read seemed to indicate that it will bring more compatibility between the newer 8,9,10 and to a certain extent 11 and 12 speed stuff. So among CUES component groups there is more compatibility of components between the various speed groups. It's not something that is magically backward compatible for things that are old style Shimano 8,9 and 10 speed.

But I still haven't looked hard for information about it and the articles I find on it are scant of detailed info.

Some of the CUES cassettes seem to indicate they are made tougher to wear longer, but that seems like it might be more just a salesman speak for writing ads, as they claim longer wear for a lot of stuff that isn't CUES.