Touchscreen, no, they needed that, Brain Training was what made the DS take off along with Nintendogs, and those games would not work the same way without touch. They were also the precursors the modern smartphone/tablet gaming boom.

3D -- I think Nintendo would actually be selling more 3DS (err ... DS2?) without the 3D to be honest. The system would be cheaper without having an expensive 3D LCD, would have a longer battery life, and would have better graphics because it wouldn't have to render each frame twice.

Also I think 3D unintentionally turns off some people from the 3DS. While some people like it, I've noticed some people's eyes take a while to adjust, so when they first play it, it leaves a negative impression (it's hurting my eyes, is not something you want to hear when someone is first trying out your game system).

Nintendo should've scrapped the 3D. I think they arbitrarily threw it in because they felt the system had to be "unique", but it would be a better, perhaps cheaper product overall without it.

The touchscreen was a good, forward-thinking design choice. 3D? Would be just as fine without it, though for some reason I don't want to imagine a world where Super Mario 3D Land can't be played in 3D.

I would argue that all systems, Ninty are otherwise like that.

PDAs and tablets came before, but they didn't remotely compare as gaming devices. Since it released in 2004, the touchscreen gave the DS at least a few years before major touch-based games were released on other devices.

Yeah probably, but DS wouldn't of sold above 100 million i think