Here's the full list of unevolved Pokémon's potential base stats with Eviolite-like boosts for every two combination of stats:
The final result is, outside of previous fully evolved Pokémon, Eviolite and any future items like it are terrible. And even then it is not very good. It needs much more utility to be useful, and all species' stats need minor to major boosts. Especially second stage Pokémon, since many of them are not too different from single stage Pokémon at this point.