I'm almost certain we'll be seeing Pokémon on the Switch pretty soon. It seems kinda odd for them to have a third game as part of the same generation on a completely different console, but I wouldn't completely rule it out. If we don't get a third game/remakes on the Switch then I'd definitely expect the 8th generation to debut on it instead.
As for new Pokémon, if we do get a third game following up from Sun & Moon on the Switch then I can definitely see that being a thing as an effort to push sales and what not. We got new megas with ORAS so surely it's possible to go that one step further. If not new Pokémon then maybe we'll just get new Alolan forms since that's also rumoured.