Octopath gave a modest boost but it remains to be seen how long it lasts, could be a one-week hiccup.

There’s that downplaying I was looking for. ;)

But, joking aside, don’t underestimate a new Mario title of any kind.

Even Mario has his limits, Mario Tennis Aces didn't exactly cause a hardware tsunami.

No its not, over 70% of 3DS sales are outside Japan, you be sure that plenty of people even on West are buying Switch because it's handheld side.

Wait is it confirmed joycons only?

From everything we've seen it appears so, there's been no mention of other controllers, everything we've seen has been players controlling with a single joycon. This screen was shown when they were playing it at e3, which shows the pro controller not allowed.

On the official game page: "Go head-to-head in 80 new minigames with many ways to play: Fast and fun skill-based mini-games that use the Joy-Con controllers in all sorts of different ways" only mentions joycons.

Pretty sure they designed all the minigames around playing with a single joycon. Which is fine if you're playing with someone else who owns a switch (and thus a pair of joycons) but man... it's a lot of money to shell out to play one game with 2 or 3 people who don't have controllers.

I'd be playing this exclusively 3-4 players and none of the people I'd play with own a Switch themselves.

There's always hope that there's minigame options such as "Pro-Controller supported only" etc, Just like there were in Mario Party 6 for "No Microphone Games". But I'm very doubtful.

That really sucks. I don't want to buy and keep up with another pair of joy cons, but I was really looking forward to this game. I might just have to buy another switch 

As Miyamotoo wrote, it's not dead, but undeniably mobiles stole a slice of casuals from it. As sales are showing, the hybrid solves the problem, giving it back enough users to remain viable.
Sony and MS don't need to understand the old portable market anymore, Ninty did the job for them finding the new hybrid market. But as I wrote, while the new concept is already working with Ninty approach, to work with MS and Sony one it will need far more powerful mobile CPU cores (GPU isn't a problem, as graphics are scaled down when using a hybrid undocked). Battery life, this is a good objection for MS and Sony approach, that's why, unlike Ninty, that didn't even consider x86 architecture anyway, they need all the possible advances in the next evolutions of Zen architecture, at least 7nm Zen 2, as 14nm Zen and 12nm Zen+ won't probably offer enough performance per watt even in customised versions for consoles, and let's not even consider 28nm Excavator. But this is fine, both Sony and MS can wait for next gen until 2020 , and possible hybrid versions could even arrive in 2021 (devs will know it since they receive the devkits anyway, if this is the case, it will follow its schedule and plans, it won't happen by surprise) if some more time for the right mobile CPU will be needed.

PS: Batteries too evolve with time, BTW.

And probably will, not just software, but also hardware. Especially parents will buy this one for their evenings with friends or their Kid's parties. Hence why this game is a good way to encroach into Playstation/Xbox homes and thus sell quite some hardware.