Quoted By:
Pokémon Red/Green February 27, 1996 Japan
Pokémon Blue October 10, 1996 Japan
Pokémon Yellow September 12, 1998 Japan
Pokémon Gold/Silver November 21, 1999 Japan
Pokémon Crystal December 14, 2000 Japan
Pokémon Ruby and Sapphire November 21, 2002 Japan
Pokémon FireRed and LeafGreen January 29, 2004 Japan
Pokémon Emerald September 16, 2004 Japan
Pokémon Diamond and Pearl September 28, 2006 Japan
Pokémon Platinum September 13, 2008 Japan
Pokémon HeartGold and SoulSilver September 12, 2009 Japan
Pokémon Black and White September 18, 2010 Japan
Pokémon Black 2 and White 2 June 23, 2012 Japan
Pokémon X and Y October 12, 2013 Worldwide
Pokémon Omega Ruby and Alpha Sapphire November 21, 2014 Japan, North America, Australia, South Korea
Pokémon Sun and Moon November 18, 2016 Japan, North America, Australia, South Korea, Hong Kong, Taiwan
Pokémon Ultra Sun and Ultra Moon November 17, 2017 Worldwide
For the past 3 gens we've had a new generation game just a year after the final title in each generation. I know Zeraora hasnt been revealed, but it isnt out of left field to think Gen 8 will be out this year or January next year