Give me one technical reason why Nintendo cannot offer a voice chat solution within the console itself. Just one.

Remember there are other video game consoles that are far less capabile than the Switch that already have this feature built into their operating system.

It's free now, but won't be free when the subscription starts.

There's also the chance that the app will be improved by the time paid online rolls around.

In the console itself?

There's no built in Mic like the Vita/3ds has built into their design.

From a technical point that renders voice chat using the Switch not possible.

You asked for just one... but here have another for free!

You are now thinking.... "but you can plug a headset into the audio port on the console, that has been taken apart and shown to have 4 rings indicating that the system is capable of supporting a mic in that jack"

Now you put your Switch into the dock at your TV....

Where is the Jack? You're holding 2 Joycons... sat on your couch... Where's the mic?

Ahh, so what you confirm that there actually is no technical reason, Nintendo just made poor design choices. Got it.

This comment actually made my eye twitch it's so bad. Congratz on that.

Ohh I'm sorry, did you think was witty or something?

Nintendo could easily choose to either put a microphone on the Switch or the joycons/pro controller, as they did with the DS, 3DS, Wii and Wii U, or put the microphone jack in a location that it's accessable while it's docked. These are choices Nintendo made that they technically were not forced into due to other critical aspects of the design that did they could not reasonably change. All of the PCBs in the Switch are custom, as is the casing. That means that they could put the microphone jack where ever they wanted. Also, considering the inclusion of a microphone would cost Nintendo about one cent per unit, it likely cost Nintendo to develop and maintain the Nintendo App on phones than they would ever spend including a microphone, there's no cost reasons either.

There are no technical reason why Nintendo couldn't have have voice chat built into the Switch. None.

What you described doesn't make it not possible , all it means is if you have it docked next to the TV  you may have a limitation in terms of how far away from the TV you could sit , this also depends on whether your using a wired or wireless mic with the length of the  cord being the limitation in regards to a wired mic. with a wireless mic you could just use a usb port.

I'm confused since the audio port is accessable from the top when docked.

That doesn't even matter. Nintendo chose to put it in the body of the Switch itself rather than in the controllers like Sony and MS does.