Oooh I just realised something.
Hikari's Pochama refuses to evolve, as most know, and was given an everstone to keep him the way he is.
Wouldn't this be an interesting point to bring up to Koharu, whose Eevee is currently uncertain of whether she wants to evolve and, if so, which evolution?
I want to also note quickly that the G-max factor preventing evolution is merely a game mechanic to prevent people evolving their g-max 'mon. It really doesn't have any lore reason. The soup merely enables and disables the factor.
ANYWAY, the point is, Koharu could potentially learn of this aspect of Pochama, and then wonder if Eevee would prefer the same.
I think that could be cool!