Comments from the Finger: The barbarian of a magitech world is a tricky thing to pin down. Ultimately I stumbled upon the idea of the Berserker Helm and binary rage changing the nature of a barbarian in the context of magitech. Hopefully this works out.
Path of the Dreadnought
The unstoppable soldiers of wartorn battlegrounds, it is the duty of the Dreadnought to break enemy lines and raze entire cities. Each dreadnought wears a magitech helmet, a Berserker Helm, which, once donned, he never removes. Each is specially engineered for him, enchanted to make him fearless and to grant complete control over his terrible rage. The helmet is the locus of his emotion, or lack thereof.
To a Dreadnought, reality is simple: there are friends and enemies, good and evil, law and chaos. The rule above all: never remove your helm.
Beginning when you select this path at 3rd level, you are fitted with a helmet which regulates your emotion and focuses your anger. Assisted by your helmet, you can summon up rage at will, and end it just as swiftly. You are unable to rage if your helmet is removed. Instead of raging normally, you can rage for a number of rounds equal to your Constitution modifier + your proficiency bonus. These rounds need not be consecutive. You can begin and end your rage as a bonus action. Your rage only ends early only if you fall unconscious or if you choose to end it. After raging for this number of rounds, you must complete a short or long rest before raging again.
At 20th level, you can rage for any number of rounds.
At 6th level, you are immune to being charmed or frightened.
Beginning at 10th level, when you use your action to Dash, you can use a bonus action to make one melee weapon attack or to shove a creature.
If you move at least 10 feet in a straight line immediately before taking this bonus action, you have advantage on this attack roll.
At 14th level, you can focus your rage into an unstoppable fury against 1 target. When you enter a rage, you can select 1 creature that you can see within 60 feet against whom your attacks deal twice the normal amount of rage damage.
Changelog: 10/26/15: Fearless now also provides immunity to being charmed.
Focused Rage deal bonus damage instead of granting advantage.
11/8/15: Berserker Helm rounds changed from 2x prof bonus to Con mod + prof bonus