I still think this would be a useful feature.  It's nice that the unit 'tab' button skips you through all the units that haven't moved yet.  It'd be nice if the City 'tab' button at the bottom skipped you through all of your cities that have either the production or training cue open, instead of having to have both of them open for the button to take you there.  When you have a lot of cities, this becomes a chore currently.

It only takes a few clicks to go through all of your cities using this button, and you get more info than if you open up the city info screen, which is a little less descriptive than the city info at the bottom of the screen.  Since I like keeping my cities busy, if resources allow, this would make things go slightly faster, since it would involve less clicking/open windows.

The 'idle city' popup will still serve it's purpose (showing you idle cities), so that need is served independently by said popup.