Listen, if the Illagers are like the outcasts of the village, why aren't they attacked by Zombies? They're obviously living Humanoids, like the Villagers.
A Zombified Illager would have the same attacks and stuff as their non-zombified counterparts. (Examples are Spell-Casting Zombies, fast zombies with axes, maybe even an ILLUSIONER Zombie, etc.)
They seem pretty useless, yeah, but WHAT IF: They had a new special drop... The Totem of Dying. It's pretty simple. 95% chance that when you hold it, it will give you a Withering III effect, but the rest of the time you could use it as a deadly weapon. Holding it gives you an effect called "Zombie Force", which makes any zombies within a 10x10 radius of you become passive and attack hostile mobs for you.
Any feedback is welcome!