It hasn't been all too long since Niantic released Generation 2 Pokemon for Pokemon GO, but it looks like the developer is already moving on. Datamining efforts of the upcoming Pokemon GO update show that Generation 3 Pokemon are currently in the works.
The new Version 0.71.0 update, which has already been uploaded to Google Play and the Apple App Store - but isn't yet available for download - contains code that lists 135 new Pokemon, all of which joined the original Pokemon game series with Pokemon Ruby and Sapphire. 73 new types of Pokemon candy are also hidden within the code, which will be available in order to evolve the new Generation 3 Pokemon. However, it's highly unlikely that the Generation 3 Pokemon will actually begin appearing on Pokemon GO's world map once the update is released, as the code is currently missing some key elements.
Dataminers have pointed out that the update still lacks the battle cries for each of the Generation 3 Pokemon, as well as the new moves that premiered with the third generation of games. The third generation of Pokemon will most definitely need their iconic battle cries before being released, and it's highly unlikely that Niantic will release them solely with Generation 1 and 2 battle moves.
At this time, the presence of this data is likely to just setting the stage for the upcoming generation of Pokemon to be released in the future. Gamers shouldn't hold their breath just yet, as there was a significant wait between the initial discovery of Generation 2 Pokemon in the game's code and their actual release. It's possible that Niantic may be able to speed up the process this time around, since it doesn't have to work on stabilizing Pokemon GO's crippled servers and finding and banning players who made use of unfair exploits. However, there are still upcoming Pokemon GO events, and in order to prevent them from being a disaster like Chicago's Pokemon GO Fest, Generation 3 may need to wait.
Pokemon GO is available now for Android and iOS devices.
Source: The Silph Road