Word is that the i3s's wider tires help with stability/dartiness on the highway compared to the i3. Unfortunately, i3s are not only more expensive and less common, but they are also stiffer and have lower profile tires so there's less road comfort.
The fender flares aren't that large on the S-model, so I'm wondering if you could just install some spacers and then run wider tires on the non-S for those wanting a more compliant ride and to save money. The i3s is running 175s IIRC, and that easily fits on a 5" wide wheel.
There's only one result on TireRack, but they have 175/60/19 ECOPIA EP600s for example, which should be very close to the i3s size but a little more comfortable ride.
Anyone already done this?