It already is, twice over: Battlemaster and PDK.
You can't make those subclasses more powerful, because that, added to inherent fighter abilities, would make the whole character too powerful (Battlemaster is already well above the curve). In 5e subclasses cannot remove features from the core class. If you wanted to make the "command" features more powerful, you would have to weaken the character in other ways - maybe d8 hit dice, no heavy armour proficiency, no Action Surge or Second Wind perhaps. And that would require a new base class since 5e doesn't allow things to be taken away by a subclass.