Not really Jon. things that this device might provide are:
State of Charge as a percentage (to 3 decimals). This is a much better way to display state of charge than the current coarse 12 bar display. It can even show the rate of discharge to instantly provide enough information for the driver to make an immediate assessment of impact on range instead of having to wait for the guess-o-meter to calculate and estimate
Volts do give you much more info on battery condition than the current 12 bar system on the outside of the SOC bars. The device can even display state info on individual battery cells giving you more detailed info on battery state and also info on indentifying candidate cells for replacement when the range has reduced.
It shows count info on charges, fast charges, kWh charged, kWh used and a whole lot of stuff that the car records but is not available through the standard software. This kind of info could be useful to anyone wanting to track their use.
Currently you can only charge to 80 or 100%. This device would allow those setting to be user selected
It could even allow for the setting of max charge rate allowing for slower charging for those with solar PV or when charging at locations with older wiring and sockets.
Just a few things I would love to see on the Leaf software but is missing right now. Will Nissan add them? IMO probably not and this device would allow complete control over the car.