I'll go short with this, I just did think about this mechanic and I think it could be very funny (maybe op in certain cases?)
Passive: Let me borrow it
The champion start with no active skills, once the champion allocate a point in a skill, it can select one ally champion and one of its skills and copy it for the rest of the match, upgrading the copied skill will upgrade it as if it was one of its original skills.
R: Ultimate Copycat
The champion cannot take an ultimate skill of an ally if not when allocating a point into this skill and only after lvl 6