1- AC and Splatoon's overlap gets way, way overstated imo. People seem to think that it's just one group of people who either work on one or the other, as opposed to "Nintendo EPD is at most around 1000 active development personnel, so there's a lot of overlap on
everything, and that isn't even mentioning overseas localisation teams" Their producers are the same (although I think this is about to change,
just look at the LEGO press release! NL and NH's director is credited as "series producer" now, but she was credited that on HHD as well so maybe not), there's an overlap of between
33 and
93 people depending on which game in the series it is, but that's far from the biggest overlap AC has with other series (unsurprisingly, given how big the dev teams are for
the past couple of games, it's
Zelda, but there are also overlaps with
Smash Ultimate,
Fire Emblem: Three Houses and
Super Mario Bros. Wonder that are larger than AC and Splatoon's)
What I
do think is that AC and Splatoon tend to alternate: Welcome amiibo came out in the year between the end of Splatoon and the start of Splatoon 2, and NH came out the year after Splatoon 2 ended (and NH ended the year before Splatoon 3 came out).
I also think the idea that they haven't even started
planning a new AC game in the past couple of years, even with just the lead devs, is maddening. It's been a massive hit! Splatoon 2 sold
ever so slightly more than NL did, but Splatoon 3's not especially doing great right now and it's in no way outselling NH, so Splatoon 4's not really in a rush to come out (imo it generally seems in need of a NL-style rethink at this point)
2- the next 3D Mario game is probably going to come out close to the next Nintendo console's launch (but god, the release schedule for the next year is
oversaturated with Mario games, with only the Another Code remake to look forward to in terms of non-Mario games so far), but it's way, way too soon for a brand new Zelda game given TOTK just released.
I also think that Animal Crossing generally happens during the first couple of years of a console's lifespan more often than not. 2020 was
late for NH to come out on the Switch given it happened around the third anniversary of the console, and the GameCube game is its own unique thing given it came out in 4 different years in 4 different regions (in one of those, 3 times)
It's probably not a
launch title, I think you're right there, that seems way too soon to me. But I think it's coming out earlier on in the next console's lifespan than any other console before, except from maybe Doubutsu no Mori + in December 2001 (3 months after the GameCube came out).
3- yeah, the Switch's successor is probably out next Christmas. When your schedule is
that remake-heavy over the course of a couple of years, yeah, it's a sign that things are slowly but surely wrapping up and moving over to the next platform.
4- Animal Crossing has released more consistently in autumn than it has in spring; the American release of the GC game was in September 2002 and the European release of the GC game was September 2004, the JP release of WW was November 2005, the JP and American release of LGTTC was November 2008, the JP release of NL was November 2012, the American and European versions of HHD were in September 2015, amiibo Festival was in November 2015, the Welcome amiibo update was in November 2016, Pocket Camp was in November 2017, and NH 2.0/Happy Home Paradise came out in November 2021.
Compare that to spring, which has only happened 3 times: the N64 version of Doubutsu no Mori came out in April 2001, the European version of WW came out in March 2006, and NH came out worldwide in March 2020.
Again, probably not an autumn game because it's not coming out immediately after the Switch 2 comes out, and it's not coming out immediately after the updates for Splatoon 3 wrap up next autumn, and personally I feel as if it's going to be around the same time as NH came out. But 2027 feels way, way too late to me. The gap between NL and NH is an exception, not the rule. We're not getting any spinoffs, we're not avoiding home consoles like the plague because they only sell 2-4 million as opposed to 11-40 million. I'm guessing 2025, maybe 2026 if it's really late (the fact that WW's title theme is getting a K.K. aircheck next game kind of reinforces that to me, because it's around the same time as WW's 20th anniversary)