Look at the recent quote up close:
With that in mind we have several services planned that I’m sorry I can’t talk about right now, but one thing I am able to mention to you is you will be able to use your smart device to chat with people you are playing with online.
And because this is a device almost everyone has we think that there is a very broad reach for this service, I think it’s a unique approach that people haven’t quite seen out in the world just yet.
Another quote from the Splatoon 2 press release:
"[The app] also allows players to match up with those friends directly in the game or voice chat with them via their smart device."
Let's break this down:
They won't talk about the online experience at all in detail, except to basically brag about the use of a smartphone for online chat as if no one has ever done it.
Koizumi assumes pretty much everyone has a smartphone, which means they are 100% tone deaf to the pre-emptive complaints of people who don't.
Koizumi talks about how unique and innovate the solution is, so that means any complaints before people have it in their hands can be pre-emptively dismissed as "well they haven't tried it yet."
Despite people wanting to read between the lines or cling to phrasing, all of their statements so far seem pretty clear that at the very least their priority is having chat via a smartphone.
All of their controllers don't have headphone jacks, which means it is already baked into the crust that the Switch will not handle headsets like other consoles do. At best they could MAYBE use bluetooth headsets, but that brings in suboptimal lag that hardcore gamers won't like either.
My conclusion: It is very likely their online chat will be via smartphone only at first, and it will take a huge backlash from the community for Nintendo to pull a 180 and realize their awesome idea is just so-so. And even then they might not, because the hardware lacks the jacks needed.