It's now possible to actually have working BERSERKERS in Medieval 2 Total War Kingdoms, as they need only to be changed into Heavy Cavalry/Mounts for the BERSERK-attribute to work without crashes!
I managed to read this a while ago in the "Call of Warhammer: Beginning of the end Times" mod-thread. Some of the guys there had solved the problem. Now when i think about it berserkers always were "Heavy Cavalry" in Rome Total War so it makes perfect sense. My goal for now is to just sit down and read about all of this regarding mount infantry - i will make the Berserkers in WotN have a fully working BERSERK-attribute.