I don't like it as a barbarian sub-class. Barbarians are already too close to being competitive with monks in unarmed combat, which really should be the monk's territory. Rage bonus damage plus resistance to damage and high HP make barbarians very tough.
Let's say the monk is AC 15, the barbarian AC 14. At levels 1-4, the unarmed, raging barbarian does a little more than 3 DPR. The unarmed monk does about the same damage, due to the barbarian's resistance, so the barbarian should win that fight based on a larger HP pool, though by level 4 the extra attacks from flurry of blows make it close and probably tip the fight to the monk - I can't be arsed to fully math it out, but it is a narrow difference. At level 5 and above it gets more interesting - instead of two attacks to the barbarians one, it becomes three to two, but then there is the possibility of stunning strike which can be a game changer if it lands (friendly save for a barbarian, though), or else more ki for flurry of blows.
And that's just against a baseline barbarian right now. Anyhow, I don't feel like this should be a close fight. If the monk can't even blow every other class away in unarmed combat, then it really makes you wonder what the point of them is.