Earlier this month, we learned that 100 new Pokemon from Generation 2 had been added to Pokemon Go. We weren’t able to catch them, but their names appeared in the code, which could only mean that an update wouldn’t be too far off.
Although Niantic has yet to announce the addition of new Pokemon to the game, an internal memo from Starbucks might have just given away the release date.
Pokemon Go: Generation 2 release date leaked by Starbucks | BGR

The source seems shady. I guess we'll see what happens.