With Cataclysm, Blizzard removed sub-2.0 speed non-Dagger weapons, citing that the only class that used them were combat-specced Rogues (warriors, DK's and Shaman all use slow off-hands). From a practical standpoint, this is understandable, however this did two things. First, they effectively barred combat rogues from transmogging matching weapons. They can't do double-sword/axe/mace, since they need the dagger in the off-hand (for shiv, poison procs, combat potency, mainly due to the speed), so that eliminates all those options. The only way to get matching weapons are with daggers. Second, for those races with +expertise racials (like Orcs with axes), they're applied on a per-weapon basis, meaning if you have Axe/dagger, it only applies to the axe, so you still have to gear for the dagger. It effectively renders it useless.
My idea? Customizable weapons. Give them a generic model already in-game (say a green or white quality weapon) so that it wouldn't require the designers to spend time making new models (these would essentially be meant to transmog over), a slightly lower item level/total stat allocation (say, equal to Raid Finder compared to Normal mode) to offset the ability to choose the stats. Pick the weapon type, sword/axe/mace, the speed (2.6, 1.8, 1.4, etc. for one-handers), and the primary/secondary stats (with options for strength based, agility based and intellect based classes). Damage range will be set based on weapon speed, so that they all have the same DPS, and you dont' get a weapon with dagger speed but hits like a 2.6 speed.
That way, rather than be required to use a dagger, an Orc Rogue could use an Axe with the speed and damage range of a dagger, but make use of their weapon racial, and say, transmog it for a set of http://www.wowhead.com/item=51439 . These sheathe on the back and look pretty badass (like all 1h weapons that sheathe on the back).
For Example:
Code:Electrowing Dagger Raid Finder Binds when picked up One-Hand Dagger 571 - 1063 Damage Speed 1.40 (583.6 damage per second) +165 Agility +277 Stamina Equip: Increases your haste rating by 122 Equip: Increases your mastery rating by 102
You could instead have:
Code:Generic Axe Binds when ... One-Hand Axe 571 - 1063 Damage Speed 1.40 (583.6 damage per second) +165 Agility +277 Stamina Equip: Increases your Haste rating by 122 Equip: Increases your Hit rating by 102
Now, whether these would be BOE, as something for blacksmiths to sell, or BOP as a profession perk, I don't know. I'm sure there are a few things I may have overlooked that would make this impractical or would destroy class balance, but whatever.