Well, im sure some people will agree with this, and some will not. But I am sure this is something that I would find very useful.
There are lots of graphics on which people WANT to see, and there is more than 90% people DONT want to see. The ability to have an item show or not show would bring back graphical diversity, seeing everyone in PMoP and FHoM is getting rather old.
Example of how the UI could look;
Of course, you could also add armor to show/not show.
As for now, I think an option for Cloak + Helmet to show or not show would be very useful, and it is part of 2 of the other mmo's I play, and it is very useful.