Pokemon Go has currently listed 4 region-locked Pokemon in the roster. This means these are the Pokemon that can only be found exclusively in certain areas. Apparently, Niantic has no plans on releasing these region exclusives to the public just yet. With the rumored generation 2 update expected to arrive soon, it seems like there will be another set of region-locked Pokemon.
According to the report from Otakukart, the current region-locked Pokemon can be found in the following areas; Farfetch'd in Asia, Kangaskhan in Australia, Mr. Mime in Europe and Tauros in North America. Based on the previous reports, these Pokemon cannot be caught outside the dedicated region. Niantic CEO also clarifies that these region-locked Pokemon cannot be hatched from eggs unless you are within the exclusive area. Which means it would be hard to complete the current number of PokeDex that consist of 151 Pokemon including the Legendary types.
Based on the sources, these are the probable next generation of region exclusive Pokemon: Smeargle for Europe, Miltank for North America, Dunsparce for Australia, Qwilfish for Asia, Girafarig for Africa, Delibird for Antartica and Heracross for South America.
It is quite reasonable for these second generation of Pokemon to be exclusive in that particular region since there are some evidences found in their model such as Smeargle that has a beret on its head and Europe is known as home of popular painters which that said Pokemon fits well, Qwillfish for Asia since it is like a fugu fish which is a Japanese delicacy. However, the list is not yet official until Niantic officially spreads the word.
Ditto was recently introduced to the game and it is now available to be added to the PokeDex. However, the mimic Pokemon is very tricky to catch as it transforms into everything in the wild especially the most common spawns. It was suggested that Niantic should consider a rework on Ditto's transformation ability making it more like Ditto in order to have an indication every time players encounter the said Pokemon in the wild.