With such massive results, it's pretty clear that Nintendo has no dated release for April because...they simply don't need it: Animal Crossing will keep on selling huge numbers in the short-mid term. Every week will look like a launch week, especially as GW itself gets closer.
For Japan this is true but I don't think the rest of the world will see a bump this big in terms of HW not such a sustained boost. I agree that they don't need to rush anything out but this year is a great year for them to continue the momentum the switch is enjoying.
Mario Kart is already on the platform though, so it wouldn't change much.
This logic has been used to a lot but it's never true. It's the same as when people used to say CoD wouldn't move any HW because there was already one released that gen before causing a big spike in sales. Sequels can still move big amounts of HW especially in major franchises. Even more so with something like Mario kart which technically hasn't even had a new game this gen.
Eh, I disagree there. A new Mario Kart would presumably have some new "hook" to it. There's also absolutely no doubt that it would be heavily advertised and would get bundles. People would eat those bundles up during the holidays. We'd probably see an opening month over 10 million again and it would easily be charting in the top ten for the rest of the Switch's life.
That's if it happens, of course.
Also depends if we're talking Japan or WW. IMO BOTW2 will be one of the biggest HW movies depending on its release. It will be advertised as the follow up to arguably the best game of all time and the game that defined the switch. It'll be fucking huge.