While I wouldn't place any money on them appearing, seeing Unova's dragons would be a welcome surprise for me. Reshiram was the only one that got any real screentime in Unova, and I was hoping we would see Kyurem once Cedric mentioned he was off to explore some ice ruins, but it never happened. Seeing them stand in the way of Lillie getting to Mohn in Ultra Space would be interesting. It would make sense with them being present in the games, and the Sun and Moon series, at least in my opinion, has been full of surprises. Again, I won't put money on them appearing, but if they do, I would be really happy to see them.