I think 3 is the right guess, for instance next year we'll see the release of Fire Emblem for Switch, that will likely be one of the best selling entries ever in the series given how much anticipation the fans have for a Home Console FE game and how popular the series has become on handhelds in the last few years, in addition to that I expect to see Pokémon by the end of the year, giving us 2 major exclusives, that would feel kinda empty for someone who doesn't enjoy one of the two series but if you add to that say Super Mario Maker 2 the three of them guarantee to appeal to almost anyone with at least one title for 2018 PLUS the side games like Yoshi, Kirby and Travis Strikes again.
Perhaps 2018 might only need 2 major exclusives given I expect Odyssey to go sold out in the Holidays and X2 coming out so late in the year that many people will be buying them in early 2018
