Isn't this already kind of indirectly reflected in the mod? Public order is to a large part tied to culture, in the form of native discontent and adds a malus or bonus to the tax income. It is far from being exactly what you wish for, but it's at least somehow present in the mod. Would be nice of course, if they could implement this more understandable and clear as a new mechanic, as you suggested.Would it be possible for culture to have an influence on taxes?
Imagine it like this: when you conquer a region, you basically only have the regional capital under your control.
If the previous faction is culturally similar to you, you can use existing structures to gather taxes.
If not, you will have to establish control over the numerous existing settlements of the native population.
Increasing your culture basically means that you either colonise the land or gain control over/make deals with native settlements.