Pretty out there, and ambitious but I think it would be interesting to play as an Undead, Goblin or Orc crew razing villages, dealing with patrols, mercenary bands, defending war camps and fulfilling destructive contracts like intercepting caravans rather than escorting them.
Factions might feature several constituent races; an Undead crew for example could have several different types of undead:
Zombies might have unlimited fatigue, high health, immunity to poison/disease effects, limited reanimation if not decapitated, and be unaffected by morale but have extremely low initiative and AP and combat stats. Perks grant abilities like increased reanimation probability, toughness and more AP? High level perks like turning enemies they kill into zombies until the end of combat?
Skeletons are like zombies, except they have (very) low health instead of low initiative, AP and combat skills, and lower reanimation rates. Perhaps they take extra health damage from blunt weapons and reduced health damage from other sources?
Ghouls have high initiative and AP, have high morale and can consume corpses to regain health and improve their morale and stats, but are fragile. Perks grant additional bonuses from consuming corpses, or making corpse consumption cost less/no AP?
Necromancers have low health, morale, fatigue and combat stats, but can cast a variety of spells that bolster and (re)animate undead (perhaps even reanimating fallen enemies for the duration of the combat), or wound/debilitate the enemy. Perks grant additional spells?
Vampires have high initiative, high AP, can teleport and can drain blood to regain health, morale and improve their stats but are fragile. Might get perks for special abilities like Mind Control, improved teleportation and the like?
Ghosts sap morale in an area around them, ignore shields and armour and are extremely evasive, but are fragile. Perks grant abilities like possession/demoralization, and life drain?