Completing a quest should automatically learn all transmogs available as rewards. We shouldn't have to choose between a cool transmog and an upgrade. This should include mail and plate for those classes that can learn it later but complete a quest early on with those type of armor rewards.
Additionally, allow us to transmog any ranged weapon into another. The reason behind this is that most endgame weapons are crossbows and so we barely get to use bow or gun animations.
Ammo can be kept as is or simply make guns only transmoggable to themselves. Adding ammo transmog could also solve this problem, as there's some of them in the game like the AV ice arrows and others could be created to have fiery vfx, for instance.
Finally, allow polearms to be transmogged into staves and vice versa. Since they share animations, it would be logical considering that's how axes, swords and maces worked already in TWoW.