With the introduction of the whole champion-system I think it'd be a great idea to have an addon for managing your tabards.
It would work something like this:
You specify a tabard that should be worn in any instance where it actually has an effect.
(There could be a priority list maybe, so that it switches tabards once you're exalted with one faction or so, but that's not too important)
and: you specify one tabard that is supposed to be worn whenever you are not in an instance where it actually makes a difference. (maybe there could be an option where you select multiple tabards and it randomly picks one, like squire does)
I got this idea because there are a couple of tabards that look quite nice, such as the Tabard of the Achiever .. but I never wear them because I know I would forget to equip my whatever-faction-i-need-rep-with-tabard when I do a heroic or something.
This can probably be done with Closetgnome or so .. but it would be really clumsy and one would have to make lots of sets or conditions or whatever. Why do that when someone else could write an addon for it? ;)