Pokémon Go Hub have announced that they have uncovered generation II data inside the 0.45.0 APK. Entire families of new monsters as well as their "candy assignments" are part of the data, which seems to suggest that maybe we're not too far out from the getting a massive influx of new monsters to catch. But it should be noted that while this is a good indication that we're getting it somewhere down the line, it is likely a bit optimistic to think it's just around the corner.
What may be just around the corner though is Ditto. In the leaked data he now has a move "transform" complete with an animation. The illusive pokémon has been the source of much fan speculation, and perhaps he'll finally start popping up in the near future. No reference as to how Ditto will be found or if there's an event associated with his release has been found as of yet.