I would love to see in-progress evolution sprites.
For example if you are 3 levels near the evolution, your Pokémon will start to manifest a change unless holding an everstone.
Same way, if your Pokémon is with enough love points to evolve, it will start to show as an in-progress evolution. For the Eevee case, it would change with the weather just to make it immersive.
For Pokémon which evolve at being exchanged, they will manifest this in-progress evolution just in battles.
I'm just a dreamer dreaming for an immersive pokemmo.