I hope they do make it in game as its another nice uniqueness to each faction.
I can think of certain aspects for example Warriors of Chaos and beastmen could have a rite based on each Chaos God but have variations for each race. I would imagine Rite of Tzeench increases winds of magic etc, Nurgle unit replenishment and possibly resilience against attrition, Khorne could give frenzy and battle buffs, and Slanesh increased recruitment vet and possibly growth boost.
I could see factions having rites for Rare units e.g. Empire has one to recruit steam tanks much like how Slann are recruited or once you buy one its put in a recruitment pool to assign it to an army.
What Ideas do you guys have?