Nice to see EAD/Shikamaru Ninja back here. He always seems to have the best detailed breakdown of Nintendo projects and teams.
Monolith's current project should probably be appended to include this unknown title
Given that we know Xenoblade 2's development started before Xenoblade X launched, it's pretty much certain now given that Xenoblade 2 is just over a month to release (so the game should probably be in Certification right now), that the majority of the development team has probably transitioned to the new project.
Of course given that we know pretty much nothing about this project, there's no way to even theorize when it could ever release. While Xenoblade 2 was able to be released in 2 years from the prior game, given that this game will likely be something completely new (and reusing the Xeno2 engine, as it was reused from XenoX, may not be an option to hasten development)
I have to say, that 2019 might be too ambitious.