100% support this. A friend of mine was telling me how they do this in DC Universe Online and all I could think about was how much I wish this was a feature in FFXI. Basically every piece of gear you acquire is added to your "fashion" inventory that you can choose from when gearing up your character for their visible appearance, separate from the actual stat gear you have on (just as in the OP).

Unfortunately, though, I fear that it's too big of a change to work within FFXI's framework. PS2 limitations, whatever. Actually I think it would just require more reworking of the game than they'd like to spend man-hours on, and since it's cosmetic they'd skip on it.