I could see them implementing Sketch, but having it function a bit differently than it did in the main series. Once you enter a battle, maybe it becomes a copy of whatever charge move the Mon you're facing has, for the duration of that battle. Or maybe permanently.
It's also possible that they don't implement Sketch, or make it a basic move that doesn't do anything special. They did exactly that with Delibird's move, Present. In the main series, the move has a 50% chance to deal damage and a 50% chance to heal Delibird. Sadly, in Go, it's just a mediocre quick move that does nothing special.