Though I like the idea, if they did make a special quest line around a unique and extremely powerful weapon, it'd be kind of a shame if it was restricted to just one class. Instead it might be nice if such a quest line and content focused around the creation of a weapon that is 'attuned' to the PC's soul, thus when they wield it, it gains bonuses and abilities corresponding to their class, skills or maybe even respond to past actions etc.