I had concerns when Blizzard first announced the way bosses would be unlocked in Patch 3.2's new raid instance, the Argent Coliseum. Blizzard has announced that while the first boss is available immediately, other bosses will be unlocked week-by-week. It's not the first time an artificial barrier has been put up for raid progression -- hello Sunwell -- so I guess I'm not shocked by it, but progression wasn't really what I was concerned about.
In our current raiding system, each boss drops a pre-determined set of loot. Some bosses drop a token which can be turned in for a piece of armor matching that particular slot, and the boss will always drop this same slot token. Thorim will always drop a shoulder token in Ulduar 10, for example.
So the issue is, with the Coliseum officially being our new tier of raiding, with gear that far outclasses Ulduar gear, and with the Coliseum bosses being unlocked each week, it means that players could get screwed out of upgrades. Your chestpiece might not be the greatest, so if you were looking forward to upgrading it, you'd be pretty crushed to find out that the T9 chest token only drops off of the final Coliseum boss -- which will only be available (at best) a month or (at worst) several weeks more than that due to RNG.
It turns out that Blizzard was thinking the same thing I was. That's why, with 3.2, Coliseum bosses all drop one of three universal armor tokens -- the Regalia of the Grand Protector, Vanquisher, or Conqueror.