Time and Havok constraints. I'm not claiming it will be perfect, however Depends on how companions are implemented. But it's possible to make them work with this mod (up to authors) There is only one true relationship system, it's defined by the engine. You have allies and enemies because of this system. Vilja and ANY other companion mod MUST use this system to become ally with the player (there is no way not to use it). Otherwise they would stand still in indifferent pose while you are being attacked by enemies. However, most mods authors don't use the Lover relationship rank, because it's useless in the vanilla game. It's up to authors to deside, will they use this rank or not, but it's just few lines of code and it won't make the mod "incompatible", so why not? I think i understand then how the mod works - quite nice indeed! :) Is it still in an early alpha or in the final testing stage? :)