Well, we have some sucky news for you folks. The good lads over at Pokémon GO Hub have datamined the dump from the latest APK, 0.37.1, and they say that there are absolutely no references, no hidden easter eggs, no subtle nods, literally nothing hinting at Ditto’s (immidiate) presence, in the code.
Apparently, there are no references to anything about Ditto, except for the Pokémon name and Pokémon family name. The Legendaries seem to have more references in the code than Ditto does.
Now, we could say that the request might be handled by a server-side code, but even that requires a handler in the client-side code, which isn’t present, either.
The only way Ditto could probably have a presence in the game through a server-side code, is if it were to come from evolutions, spawns or walking, but considering the length Trainers go to, if any of these were true, somebody would have landed a Ditto already, and since that hasn’t happened, we can safely say that Ditto indeed isn’t present in Pokémon GO, yet.
Whatever references it does have, including Pokémon name, Pokémon family name, and attacks, are all merely placeholders. John Hanke, the CEO of Niantic, did kid about Ditto being hidden in the game at TechCrunch’s Disrupt, but it seems like that probably was just a joke.
Of course, along with the Legendaries, Ditto will eventually come forth. We don’t know when or where, or how, is all.