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Currently, we know of 28 pokemon. Assuming there's only 100 pokemon added this gen, we know over a quarter of them.
If we assume that-
All starters get two evolutions
Fletchling get a middle evolution
Spritzee and Swirlix get an evolution
Litleo gets two evolutions
Clauncher and Skrelp get one evolution
Noivern gets a prevolution
we're working with 42 pokemon.