There is tons of possibilities for enemies they can add, even minor less known xeno races in 40k lore could be main threats in other settings in their own right. But I doubt they add those probably focus on chaos and tyranids. Orks would be amazing to fight that are just too fucking awesome.
Like The Slaugth for example is a straight up horror race, when they speak it's a mish-mash of the voices of all their victims final moments.