I'm in the 2019 boat as well, but at the same time, things are looking very bloated for the end of the year, so unless they announce a slew of 2020 games at the Direct in a few weeks, they are going to need stuff to pad out the first few months of the year. Not saying that that Animal Crossing could be one of the those titles, but something inevitably is going to slip.
Stuff happens. Look at what went down with Metroid Prime 4 and the all but confirmed Metroid Prime Trilogy HD collection. It was all but confirmed to appear at The Game Awards in December, but then ended up a no-show. A month later, we got the Prime 4 developer change announcement. Sure it's unlikely something catastrophic happened since February, but it is 100% within the realm of possibility something could and Nintendo would just have to take a hit in their stock rates.
It's just good to keep an open mind is all. Hype responsibly.
Like said here, if they would delay the game, Nintendo would have had already said anything
about it. They know that Animal Crossing fans waiting for any informations, they also know
that E3 is coming and the hopes and hype of said fans are getting high. Besides, all sources
still saying 2019. Even Nintendo themself. If there would be any delay, they would have
change the 2019 into TBA already.
Also, Metroid Prime 4 had a good reason for the delay because of the developer change like
you said, Nintendo wasn't happy of how the game looked so far and that's why they wanted
to start new from the beginning. I can't imagine the same thing happen with Animal Crossing.
Pretty sure whatever team is working on AC wouldn't fail so much that Nintendo would say
"Nope, don't like that. Make that again but better".
After all, just because there are a bunch of other games doesn't mean that AC has no
chance to coming out this year too just because there aren't any news of it out. After
Mario Maker 2 got it's own Direct and Smash doesn't need like the half of the Direct time
anymore to announce something new, with that, they have enough time now to cover AC
on the E3. Also, who said that they can't be two games coming out in one month? Let's
say one game comes out at the beginning of a month and the other one at the end of
that month. Pretty sure that this would work too. For example: Animal Crossing comes
out at the beginning of October and Luigi's Mansion 3 at the end of October (because
Helloween). Guess fans wouldn't drop the one game for the other one, people can play
more then just one game.
I believe in a 2019 release. Not because I can't wait any longer for that game (I'm honest
here), but also because there are no reasons right now for a delay. And who knows? Maybe
Nintendo never wanted to announce the game back then in September 2018? Maybe they
wanted to announce it in that Direct from February 2019 with gameplay and planned to
show more of it at the E3? And the only reason of why they dropped that information
back then was because of Isabelle getting into Smash, which was about to come out
a few months later and Nintendo knew that AC fans would ask where a new AC game
for the Switch is? Maybe they wanted to keep the hype with this? And now they have
to change the plans and announce all informations on E3? I don't know, I guess there
are reasons why it is how it is. All we can do now is waiting, as much as it sucks.