Mega Evolution is coming to Pokemon Go and will be available in the latter part of this year. The mechanics of Mega Evolution will be different and unique to the play style of Pokemon Go according to the developers during the Pokemon Present live stream event.
According to the official Pokemon Go Twitter account, Mega Evolution will be acquirable in the wild.
Unfortunately, the information is scarce and very limited. As of this writing, all we know is that Mega Evolution is coming to Pokemon GO but how it works is mind bugging. We are also not certain if all the Pokemon that is currently on your rooster can Mega Evolve or will it be exclusive to certain specific Pokemons.
Be sure to stay tuned and we will keep you updated in regards to this matter.