So, most of you probably know this, but if you dont, to this website: https://bulbapedia.bulbagarden.net/wiki/Z-Move
Z-Moves are very powerful, but how can they be implemented into Pokemon GO, well I know a way that could be very cool, but also kinda complicated, so these are the made up requirements for a one of your Pokemon to gain a Z-Move.
First, the Pokemon must have been in your Pokemon Inventory for at least 6 months, then must have won at least 75 pokemon battles (PvE and PvP), then must have been a buddy pokemon for at least 25 KM, then you must obtain the right Z-RIng, which can be obtained via an Item called the “Z-Box” or a 1.1% chance of thru a Pokestop, but the Z-Ring is random in both cases, the Z-Box is purchasable for 750 Pokecoins, then you go into your Inventory, open the box, and obtain a random Z-Ring (ex. Gigavolt Havoc), the Z-Move can only be used once per battle (PvE and PvP) and will do massive damage regardless, and mostly only final evolutions can use Z-Moves.
I hope niantic implements this soon!