2018 is a great year for secondary franchises. It's the perfect time to add games from the series' that don't get as much representation. I'm pretty sure we'll see some form of Metroid in 2018, even if it's not the new prime. I think we'll likely see a new Animal Crossing game, because it sells gangbusters every time and it's been ages since the last one. We might see a new StarFox and we might see a side Mario title.
A new Smash or Smash 4.5 will probably be announced at E3 I think, but maybe in the January direct. Smash is a great announcement because they can announce fighters all year long.