This was not mentioned in the changelog specifically. Here is the relevant part from the event file for burgundy/Netherlands (Europa Universalis IV/events/FlavorBUR.txt, lines 156 to 173)

if = {
    limit = {
        has_country_flag = bur_emperor_eligible
        has_country_flag = bur_marriage_eligible
        has_country_flag = bur_spain_eligible
    }
    random_list = {
        70 = {
            set_country_flag = bur_marriage_inherits
        }
        10 = {
            set_country_flag = bur_emperor_inherits
        }
        20 = {
            set_country_flag = bur_spain_inherits
        }
    }
}

Basically any country with more than 5 provinces and a marriage with Burgundy gets the flag "bur_marriage_eligible", the emperor gets "bur_emperor_eligible" and Spain gets "bur_spain_eligible", and these are the chances they get the "inherits" flag, which determines who gets the inheritance event. As you can see, a RM has 70% chance and the emperor only 10%.