How about making The Black Pit actually have a fighting pit? If fighting, a player would need to choose one warband member to enter, and opponents could be live PvP or AI fighters. Perhaps players could also visit as spectators and wager gold or shards on the outcome of a fight. Some of the AI opponents could just be copied from existing characters like AI warbands are, but perhaps with the names changed. Other AI opponents could be test characters for future faction releases, such as orks, dwarf trollslayers, etc. and other creatures might be stand-alone things like an ogre, troll, or minotaur (actually I'd like to play as something like that in the regular game, though I think such things might have to be limited to a single character, as a herd of 8 Minotaur would be pretty broken). Perhaps some AI opponents could have multiple members, if they're something like a gang of goblins and snotlings.