I'm pretty sure the lack of self centering is a result of stiffness in the rack, not an inherent design feature of the i3. But I would like to hear from someone (anyone!) who says their i3 does self centre as you'd expect. I've read/seen plenty of reviews which mention excellent feedback from the road but I get virtually none.
For my entire driving life (35 years/50+ cars) I've never driven anything that doesn't self centre unless it has a fault. On all other cars you can tell if your alignment is out by the car pulling to one side or the other, or tracking straight with hands off the wheel. My i3 pulls to the left, pulls to the right, or goes in a straight line purely depending on where the steering wheel is left.
Come to think of it, I regularly drive on the A14 in UK - it's a road heavily used by large trucks and has quite severe dips where the truck tyres have worn the surface down. In my partner's VW Polo you barely notice when you go in and out of them, in my BMW 435d with wide, staggered wheels it's definitely noticeable but easily dealt with. In the i3 you have no notice then suddenly the car will veer off in one direction and need to be caught. It's like there is absolutely zero feedback from the wheels to the steering wheel so you don't feel the wheels being pulled slightly to one side and naturally correct it.