According to the changelog posted onto Facebook by Niantic, “Over 80 additional Pokémon originally discovered in the Johto region can be caught.” They also add that there will be gender-specific variations of select Pokemon that can be caught. As per our previous report, there will be new encounter mechanics, new berries, new avatar outfit and accessory options, and bonus candies for catching evolved Pokemon.
There will also be new Poke Ball and Berry selection carousels added to the encounter screen. The update should also bring about improved connection stability for the Apple Watch version of the app, as well as your usual host of bug fixes and whatnot. The update will bump the game up to version 0.57.2 for Android, and 1.27.2 for iOS.
As for the promised PvP battles and trading system, those are expected to arrive in future updates so hold on tight as they should hopefully arrive in the near future.