Just an idea, inspired by the new Warlock questline to get different green fire.
To me, half the fun of the latest legendaries is the diffent graphical effects and uses for the items, even outside of combat, like the Rogue wings or Tarecgosa mount.
How about have some kind of REALLY cool graphic effects/style minor glyphs for classes, but to keep them a little more interesting and maybe rarer, add a (old) legendary style questline in order to be able to unlock them so people are wowed/impressed when they see them.
Just as some examples, you could have a whole questline that unlocks a Scorpion model to replace a Druids cat form, or Demon wings that you can use as a flying mount for Warlocks.
I know the wouldn't be as great as a weapon too, but still think people might like them if they were awesome enough. Any other examples/idas/input?