I'd like confirmation this is true because Hindustan didn't function as a union in previous patches (even though it should have).
I do believe it has always been this way, but it's a little complicated.
India now has 5 culture groups: Hindusthani, Eastern Aryan, Western Aryan, Dravidian, and central Indian. When you form Hindustan as ANY Indian nation, you get Hindusthani as union culture, giving no penalties. This would be in addition to the culture you originally start with.
For eg, Vijayanagar is Kannada (part of Dravidian), so you get:
Primary: Kannada
Same culture group: Rest of Dravidian
Culture Union: Hindusthani
In screenie 1 you can see Hinduthani culture highlighted giving no malus. In second screenie you see Dravidian culture highlighed, where you get reduced malus from same culture group.
So the optimum strategy is to form Hindusthan with a non-Hindusthani culture country to get the least malus on the max number of provinces.
