The most obvious improvement imho is improving the ridiculous 12-bar "fuel gauge/miles remaining" indicator. I can't be the only one who is tired of the number jumping around and/or being way off, even if it is in a "conservative" direction. It should show (graphically) a measure of kilowatt-hours remaining in the battery, an amount which of course always and gradually decreases (ie, does not jump around). Then it could also show (again, graphically) a "normal curve" going from the fewest miles (or most pessimistic range) to the most miles, with the average in the middle and perhaps an indicator of the estimate driving in the current conditions.
It could be done without any numbers at all, really (as most cars have done forever), or only present numbers when it gets under a certain amount. The "world's" fascination with the digital, the numeric, and exactness has gone too far, and this is a perfect example of where it is completely inappropriate (ie, in an inexact setting). Analog is still beautiful.
Anyway, I suspect there's a whole forum dedicated to this topic, but I'm throwing it in here for good measure.
Other features include an easily accessible mute button, allowing the charger door to be opened without having to go back to the door (arrgh!) and reach in (it could still require the FOB to be nearby), and (not car-related per se, but) a map online somewhere of dealers which have ChadeMo quick chargers installed and when others are due to have them installed.