-Combo cast allowed the user to create ability logic which would activate certain abilities based on user defined criteria with a single button.
-Combo sounds is a rogue/druid addon that gives musical indications when you should be using combo generating or finishing abilities.
-The fret bar concept from the bard hero class is a graphical display much like the interface of guitar hero, showing the buttons you have to be pressing and will have to press in the next few seconds.
My idea would be to have a fret bar-like display which tell you the abilities you should be using.
The user would configure abilities they need to use depending on criteria such as target health levels or time until a cooldown becomes available.
The addon would then 'predict' the buttons the user has to press in the near future and display those on the fret bar wich could be suplemented by sounds (or musical scores).