I've read several pages of this topic, but not all. Several observations:
- Like many rear-engine cars I've owned, the i3 can benefit from lower tire pressure in front. BMW's spec is a bit high for my taste and the high speed dynamics of the car, probably for reasons concerning range, cornering, and potential pothole damage. I am currently running 27 psi in the 19" tires, and the high speed stability is much better - almost normal feeling. Of course this pressure is at the peril of potential pothole damage, but I much prefer it overall. It doesn't seem to affect cornering adhesion in most normal driving - maybe if you're racing it.
I feel the i3 steering geometry could benefit from more caster (as someone previously mentioned). This would provide more mechanical self-centering at speed, and a bit more weight in the steering feedback. Unfortunately, this is not adjustable on most strut type suspension, including the i3. It is what it is, unless BMW changes the setup.
The 20" tires are more sensitive to steering input (and bumps), due to the lower profile / stiffer sidewalls. That's why I got the 19" tires.
As the tires wear-in a bit, the sensitivity to road surfaces, joints, crowns, etc. gets a bit better.
Driving with elbows on the armrests, rather than suspended from the wheel, helps maintain stability at speed.
All that said, I don't consider the dynamics dangerous. It annoyed me a bit at first until I became more accustomed to it and lowered the front pressures.