Not everything needed for Gen III’s Pokemon is in the game yet, but it should all be rolled out in updates by Halloween.
A special Halloween load screen is also hidden in the update. As you can see, it features Gen III Ghost Pokemon like Dusclops, Banette, and Sableye. The game will also play Halloween music (a Lavender Town remix) whenever Niantic decides to flip the switch:
With this news, we should expect Gen III TCG products in the spring and summer, as we did with Gen II when its Pokemon came to Pokemon GO. Expect boxes, pins, and decks featuring the Regis, Latios, Latias, Kyogre, Groudon, Rayquaza, Jirachi, Deoxys, and other Gen III Pokemon.