Of course not the tracking 3D. I mean the other things, like the N3DS's CPU, and a higher resolution screen (360p maybe) with the corresponding increase in GPU power, combined with the same size as the N3DS.
That could have been done. The 3DS sips power and has a tiny battery inside. Having two analog sticks and triggers could have been done too, as well as a decent plastic shell.
Again, that CPU did not exist back then. It was not an option in 2010.
And while they could've used a higher resolution screen, it would've greatly decreased overall performance (which was already an issue with having to render the game twice for S3D). The GPU was already clocked as high as it could possible go, and they were already fighting to pull off 2-3 hours battery life with S3D... What do you think an even higher resolution screen would do?
Releasing a console is a delicate balancing act of price, performance and size/heat dissipation. In a handheld, it's even harder because you have to balance battery life on top of that.
If there is one thing that I think Nintendo got wrong with the original 3DS design, that could've reasonably been addressed, it's the decision to target such a small form factor to begin with. Instead of targeting the DS Lite/DSi form factor initially, they should've targeted the DSixl size first (basically releasing the 3DSxl as the standard model in 2010/2011), stuck a larger battery in there and worked on shrinking it down later on. They also should've included the N3DS Zr/Zl buttons and analog nub to begin with as well (but then again, shoulda, woulda, coulda).
