It’s an idea predicated and rooted in all of the mechanics and concepts of the game.
Granted being an Undead or Orc warband that loots, plunders and fulfills offensive contracts against villages/merchants is a very different vantage from a group of mercenaries that works on their behalf, but is ultimately similar in terms of actual gameplay; different opponents, different premises for combat, different situations, but ultimately it’s a skirmishing throwdown with your guys against theirs.
Hell, if they made this an expansion to the core game I would not object at all.