So do you think we will see a 2nd pilar 100% portable device in the future from Nintendo?
Actually, I do. I think one thing to keep in mind is that if the Wii U was a success, continuing on with 3DS for a year or two longer would be fine because this is still that console's typical generation cycle. Switch was intended to combat the losses of the Wii U as Wii U was cut mid generation for that system so the reason we even have 3DS and Switch at the moment instead of let's say...the next Nintendo portable, is because 3DS's life cycle is not dead and it didn't heavily flop like Wii U's which got cut early.
As I mentioned earlier in this thread, the system itself is not as portable as the smaller systems and it lacks the dual screens which have been such a huge boon for gaming on a handheld, especially games like Pokemon, Animal Crossing, and Zelda. Switch is larger, and although it is portable, it's still not as portable as simply putting something in your pocket. You can just close the screen as well which offers screen protection.
You can say that "but you can place the switch in your pockets!", yes, you can, but the screen won't be protected and that's one pocket more than just a typical portable. Not just that, but you'll have to deal with two devices in the other pocket with analog sticks jutting out which will be uncomfortable.
The Switch is a portable system, but it's not a replacement for the much more portable handhelds Nintendo generally makes. 3DS is still in Nintendo's typical handheld cycle cause it didn't fail, so it'll continue for a little bit longer.