Last July it was revealed that dataminers had been digging into the code of the latest Pokémon GO update and had found some indications that Niantic is preparing a new survey to decide the next protagonists of the next Community Days. Specifically, the candidates (for the month of August, in theory) would be the following:
At the end of July Niantic surprised us by confirming that August’s Community Day would feature Magikarp, so no Pokémon from the previous list found in the code was chosen. As you know, the September Pokémon GO Community Day is next, but at the moment it is unknown who will star in it.
For this reason, many players are speculating that this list may be used to vote for one of them to star on Community Day in September (we remember that the last time a voting system was used was between Gastly, Sandshrew, Squirtle, and Weedle; Weedle being chosen winner and Gastly second).
However, there would also be another possibility and that is that as many of you will remember, in January of this year Piplup starred in the Pokémon GO Community Day (before the pattern was changed, it was alternating between initial and non-initial Pokémon). So it could also be Niantic starting over, which means Snivy would be the next Pokémon.
In summary, the two options that are being considered at the moment is that the September Community Day comes out between the list made up of Caterpie, Charmander, Grimer, and Porygon or Snivy. Obviously none of this is safe, so there will be no choice but to wait until Niantic announces it officially.