Hey, long time lurker here, thought I’d share my thoughts. I think it’ll be 2019.
They typically like to announce new gens around the start of the year (XY in January, SM in February) so that they can use the entire year to build up hype. For the very first game on a home console I imagine they’re really gonna stick with that this time.
The latest a modern new Gen was announced was Black and White in April, with a fall release, but I think that’s a different case. Arceus was revealed a year prior to that, so gen 4 was long done, but here, we literally just got Zeraora yesterday and the anime’s still got a long way to go before it can wrap up and move on.
The only way I can see it coming out this year is if it’s a Kanto reboot, but I don’t see that happening just yet. They’ve never opened a new system without having a brand new gen game to launch it off with and I can’t think of any reason for them to stop that now, especially when they have a golden opprtunity to remake Kanto in 2021 for their big 25th anniversary celebration (which gives them time for Gen 8 in 2019, and Sinnoh in 2020)