I felt compelled as another 6'4" i driver, to put in my 76 inches worth ...
We have a 7 and 11 year olds, the younger sits in a booster and hasn't ever had trouble, even with me in front of her. I guess that a backward facing seat would fit, unless the person in front has the seat all the way back and reclined (even for me, I don't need to recline in the i like I do in other cars because of it's tall stature, so it should be less of an issue). Before we bought the car (I do this in any car to judge space), I set the front seat for me to drive comfortably, and then sat in the seat behind it to see how legroom was. Headroom is great, legroom was a little tight, but not impossible.
In the old days, we were able to fit a rear facing baby seat in a Ford Focus ... and I don't think, front to back, the i is any smaller.