Clever concept that might give way to some interesting puzzles particularly if you add different materials to bounce off of. Its sort of a simple golf game, I'd measure someone's score by how many shots it takes to get the cubes.
Screen Shot:
I would make it so that the FPS pointer is where the cube lands. So if you point to a place it will adjust the vertical velocity to make it land at the correct location using the quadratic equation. Its annoying to have to point very far up into space to make the cube land in the correct spot and you lose site of the target.
Also, I would smooth out the transition to the new location you move to after the cube lands. So I'd just run the code:
CurrentPosition = Lerp(CurrentPosiition,CubeLandingPosition,Time.deltaTime * 5)
Then its a lot easier to understand the concept that you are moving to the place the cube lands.
Its an interesting concept, hope it works out.