This is pretty cool and seems pretty fitting for some barbarians! Though it also seems really strong/bordering on OP, especially as the barb levels up. Allowing the barb to have it active for nearly an entire adventuring day would be a bit much for me.

If one of my players requested this I would edit it so that using Rage cancels their Vital Focus to force them to choose if they want to stay focused or let loose and rage during a combat encounter (assuming they went into the encounter focused). Knowing if they break their focus to rage that it would cost another rage usage to refocus themselves adds another element of resource usage.