GameFreak has confirmed that the year after Let's Go they would release another mainline title, so unless it's Let's Go 2, it has to be the 8th gen.
They didnt officially announce the actual game though.
I dont remember "Pokemon 2019" to be officially announced as an actual title, until they do - its just heresay lol.
When you type in Pokemon 2019 - Detective Pikachu and the new Mewtwo movie show up in the results.
If it was actually announced, it would be #2 on my list.