Nintendo's got a stacked 2019 so far. But one thing I was disappointed about during the E3 Direct, was the lack of actual "New" game announcements from Nintendo themselves. The biggest release that was originally for 2019, was pushed back to March, and the only thing new was a teaser for a BotW sequel. To me this doesn't really add up since according to Emily from ResetERA, there's at least a few more first party games for 2019 Nintendo has yet to reveal. Knowing Nintendo, they don't need E3 to announce all their games, so the stuff that wasn't shown is either being held back from announcement due to not being E3 worthy (things like Digital titles, Labo, ports, etc.) or some of them is slipping to 2020, leaving them to be shown off at a later date. I'm wondering when Nintendo will show the rest of their hand for the year October-December look pretty light on releases so far, so that might be a good opportunity to bolster them a bit. And I predict another Labo Kit will be arriving very soon, perhaps August.

Like I said, I think Nintendo now only views E3 as a place for their big guns only, so that's probably explains the lack of new announcements despite there still being unannounced 2019 games

Wouldn't be shocked if they do some Treehouse announcements, but it will probably be ports

True, They shadow dropped Arcade Archives DK and Sky Trooper last year during Treehouse, and the year before had a few 3DS announcements. It wouldn't surprise me if a game or two was announced tomorrow.

What they haven't revealed for 2019 yet are probably things like the Metroid Prime Trilogy and Wii U ports that don't need a 6 month+ cycle of hype/anticipation/advertising.

Nintendo published titles for the rest of the year:

Undated:
Luigis Mansion 3

June:
SMM2
Cadence of Hyrule

July:
DQ Builders 2
Fire Emblem Three Houses
Marvel Ultimate Alliance 3: The Black Order

August:
Astral Chain

September:
Daemon X Machina
Link's Awakening
Dragon Quest XIS

October:
Nothing

November:
Pokemon S&S

December:
Nothing

Already pretty stacked, I could see a couple of minor games.. a port or two to add to the lineup.

I could also see another Labo Kit, as well as a few eShop only games to round out the last 3 months as well.

probably a Wii U port or two or some smaller games i'm guessing since the rest of the year is pretty filled out already outside of October and December now since Animal Crossing got delayed and Luigi's Mansion 3 still has no date (but I assume it'll be an October game)

there's also plenty of other undated things like Panzer Dragoon Remake, The Witcher 3: Complete Edition, etc

I could see more big third party ports getting announced in a later direct and then releasing a month or two later like DOOM back in the September 2017 direct as well

Super Mario Odyssey DLC, of course!

I think Luigi's' Mansion 3 will likely be October for two reasons. 1) If it was coming out earlier, we'd already have a date or window for it. 2) Ghosts, spooky haunted hotel, October/Halloween. It makes too much sense. Think of all the marketing possibilities!

It could be, but she's got a pretty solid track record, so I'm inclined to believe her until proven otherwise.