Pokemon Refresh with HD Rumble.
There are already feedback mechanisms while petting pokemon with sound effects and animations for the on-screen trainer hand when petting non-corporeal ghost types like Gastly or sludgey pokemon like Grimer. You can burn your hand if you touch part of a pokemon that's on fire or shock it if you touch Pikachu's cheeks. And if you hold your hand in the right place for certain pokemon, they'll reach out and high-five you.
I think all of these features were developed with the Switch's HD Rumble feature in mind, to allow the player to feel like they're actually physically interacting with their Pokemon. Which also would give credence to the rumors that Pokemon Stars or some other kind of extra version/sequel of Pokemon Sun and Moon will be released for the Switch. Thoughts?