It would be nice for the barbarian to have alternate option to the rage in core.
A barbarian could have Fury as a class signature feature with Rage being one of the available furies (rage power could remain the same).
Even if Rage is the only available Fury in the core book, it would open a easy door for later supplements having slightly different approach to the barbarian's fighting style (desert dervish, steppe rider, amazon dual-wielding warrior etc) without having to adopt a prestige class.