Here is an idea that I had a few days ago. There would be three new weapon rarities (steel, crafted, and alien).
Alien rarity is used on weapons that are either based on or actually alien weapons (i.e. line rifle). Alien weapons far exceed the power of exotics but are banned from the Crucible as they "taint" the meaning of the Crucible. Alien weapons could drop from any mob, but would be the same level (and same stat level) as that mob.
Steel weapons are weapons made specifically for the Crucible. They out-power exotics and are on par with Alien weapons.
Steel weapons would be obtained after certain milestones in the crucible (aiding to obtain 100 victories). The milestones would have to be looked at to make sure that afkers cannot obtain them (but anyone who actually participates can).
Crafted weapons would be on par with Exotics, however are a little different. They would be obtained much like weapons from exotic bounties. Player's would get the weapon from a drop but would instead get a schematic. After they talked to the weapon smith they have to go through a list of parts necessary to complete the weapon (i.e. deconstruct 5 legendary or rarer auto-rifles for precision barrels). These weapons would still be partially random, and players would still be required to work for them.
Quite honestly I doubt we will ever see anything like this, but I'm putting it out there anyway. If you have any constructive comments/ideas please feel free to leave them below.