With the release of a new 3DS, we can expect a new Pokémon game to appear, like one that will focus on Necrozma.
The question is, what will happen after that? Well, there are two possible scenarios.
1.Scenario 1: Pokémon on Switch.
Since Pokémon games take about two years after a console's release, next gen can appear on Switch in 2019.
2.Scenario 2: Pokémon on dedicated handheld
In this scenario, next generation would be exclusive to N3DS, but released on a new console.