This has been the most frustrating thing in the game for me. I see a piece of gear that looks really nice that I'd love to use only to find out that it's for another class and the closest look-alike that my current class can use is a different color and is undyeable, if one even exists.
The last official word on this the idea was rejected because the developers felt that it would be confusing for new players to see people running around in gear that doesn't match their class.
However, these days we have tanks that wear robes, DPS wearing heavy plate and healers in bikinis. It's safe to say that that ship has sailed and is no longer a suitable reason to continue to class lock glamour items.
There should still be class-specific gear, but it should be only a handful of sets unique to each class (i.e. lvl 45 and 50 job gear).
This game has done so many things right and hasn't been afraid to change with the times. Well, the times have changed once again and this also needs to change.