If it is true, it is possible that Sven, the reindeer, could have been an orphan just like Kristoff. Sven’s mother could have been killed by the ice harvesters and that is where Kristoff could have gotten his reindeer coat. This would explain why the two have this unbreakable bond.
Kristoff could be wearing the coat all the time to remind Sven of his mother’s smell. The theory becomes more believable when the bond between the two characters is highlighted.
Kristoff also has this unusual behavior of talking on behalf of Sven that could be considered as a borderline dissociative identity disorder. If this is true, this is a mystery Anna has to unravel on the next film.
While only an astute observer with just too many time to spare can really focus on this stuff, everything at this point is speculation because Disney has yet to make any official statement or announcement regarding the possible plot for “Frozen 2.”