shoichi on 21 June 2017
I think it depends how early Gamefreak started on the new generation after Sun and Moon and how early they got their dev kits. 2018 is somewhat possible. Also maybe this is the 'remake' generation on Switch? Which means they can hold off on a new generation and just create a game like Pearl and Diamond in HD with a reimagining of the game.
2007: Diamond and Pearl (new generation)
2009: Platinum ('third' game)
2010: Gold and Silver (remakes)
2011: Black and White (new generation)
2012: Black and White 2 ('third' game)
(no remakes)
2013: X and Y (new generation)
2014: Omega Ruby and Alpha Sapphire (remakes)
(no third game)
2016: Sun and Moon (new generation)
2017: Ultra Sun and Ultra Moon ('third game')
(no remakes announced yet)
