Personally, I am of the school that says every old world nation would be better off having their own armylist, rather than having to field them in another army. I mean, I know that Kislevites used to be Imperial in 5th-edition, but surely one can give them enough unique units to make them their own crazy faction...I remember an exceprt from Beasts in Velvet that the Red Star Kislevite Underground had radical ideas about worker ownership of the means of producton...The Empire wields a hammer, Kislevite wields a...sickle?
At any rate, we would have Kislevite Strelets, who have halberds and handguns; this combo provides a +1 to-hit bonus due to the bardiches being usable as gunrests. The unit has the option to carry a Gulai-Gorod, a movable fortress which prevents marching but allows the unit to be treated as being in hard-cover.
I could see them also having fear-causing light cavalry with flails ("Oprichinki"), their Kossars and Winged Lancers as normal, some variant of a war wagon...
As for casters, there are the ice mages of course, perhaps some sort of shamanic human that could use hallucinogenic mushrooms, maybe a melee hero with some minor spellcasting ability; alternately, a Baba Yaga-inspired witch in a flying mortar-and-pestle (or Terror-causing hut with legs)...
