Since a lot of the early alchemists came from the Muslim world, maybe something focusing on that. Lots of units that use explosives and chemical weapons but also buffs and healing potions. Maybe some kind of tension or outright sectarian conflict within the region between the alchemists and magic users. >>96013109
A magic system revolving around trapping spirits in various vessels would be a neat take on the genie in a lamp/bottle trope. Using a army with both them and alchemists you could have djinn and tonics