Since kimi does have a tone of familiarity to it, I think that kind of subtle meaning is a bit lost in translation.
It also explains why so many boy bands and love songs in Japanese use kimi instead of other ways to say you (anata being too neutral and omae being more of a confrontational connotation). So the fact that they know each other without quite knowing each other through their switched body experiences would contribute to how they address each other. I havent seen the English dub of the film (assuming there is one already or one in the works) but when I watched it in Japanese I was wondering how they would handle the scene where Mitsuha is in Takis body talking with his friends at school and confuses the different words for [I] and addressing oneself as one would depending on their age, gender, and who they`re talking to.
In English theres really only one way to say [I] and [me.] Perhaps theyd handle it like they did in a certain scene of Ouran High School Host Club where they changed the dialogue to fit the core concept of the scene as opposed to trying to remain perfectly accurate to the original Japanese source text. Haruhi (who spends the whole show in disguise as a male student) says shell start addressing herself as [ore] instead of [watashi] from then on to be a more convincing boy in the original Japanese version, but in the English dub they changed her line to [Ill just call everyone dude and bro now!]
Perhaps they(ll) have Mitsuha call one of Takis friends something she`d normally call her girl friends and have them look at her strange until she settles on [dude] or [bro]…