"Games will be able to give away clothes and accessories just like Achievements," Musgrave admitted, being sure to vaguely note that such a feature would come "in time." As far as corralling developers' interest, Law is optimistic, making mention that their team is "currently working with multiple partners who have expressed interest in using Avatars."
It's either unlockable Avatar apparel, being able to change clothing colors or allowing us to put our Vision camera creativity to good use. Those are your options, Microsoft. Your call.