Isle of Armor Spoilers!

There is no Galarian Dustox or Beautifly but Wurmple gets a third evolution which is a pure Dark type. Then when it evolves again it becomes a Dark and Poison type.

Next there is a Galarian Starly line which is Flying and Poison type. When it evolves to Staraptor it gains an ability where if it makes physical contact with someone. It has a high chance of poisoning the target.

Galarian Litleo line which is a Fire and Psychic type.

There will be other new Galarian forms and other new pokemon.

Mega Evloution is coming back. You get the Key Stone from Mustard once you beat the story of the Isle of Armor. However if you have not beaten Leon he will say to come back when you have completed your Gym Challenge and he will reward you for your efforts. This is so you do not have Megas during the story of the game.

You get Mega Stones from the depths of the cave in the back of the map. As well as rare rewards from certain raid battles.

You can get more Kubfu once you beat the Isle of Armor story and you have finished the Gym Challenge and beaten Leon.