Should be very doable, but salvaged i-MiEV packs are much harder to find than LEAF or Volt modules, and you'd need to take apart the pack and do a different voltage and BMS anyway unless Nissanitsu finally releases their V2G/V2H appliance for the US market.
There is a guy in Australia who started doing it about a year ago, I'm not sure where he is at. The website is down right now, I think the thread is here as it started when he got his battery replaced and kept the old one - http://forums.aeva.asn.au/forums/imiev-battery-replacement-warning_topic4653.html
Thanks, the quick bit I gleaned from that discussion is that the 5700 Aussiedollar price is below $4400 'merican money for a voluntary battery replacement. That's much better than I expected, coming to exactly $1/Ah at the cell level.
