They just released Xenoblade 2 late last year and are still developing the story DLC. I think it would be cool if they did announce it next year, but probably show more concepts than actual gameplay.
And I remember E3 2014. While I consider it a great event, it didn't do much for the Wii U so whether a presentation should be this or that doesn't really matter. I mean, E3 2008 was not stellar for Nintendo yet 2008 was their record-breaking year with the Wii. Not all great presentations correlate to great sales or vice versa.
Yeah, but a lot of that stuff will be covered by smaller teams within Monolith Soft. I wouldn't be surprised if they will have been working on the new title for at least 2 years when E3 2019 comes around, and Monolith Soft isn't afraid of showing early footage (They showed XCX in Jan 2013 and it didn't release until Dec 4 2015). They also announced XC2 in Jan 2017 and the Switch didn't even come out until March 2017. I think it will be there.