Lots of people are saying on this topic like they did on the 24 vs. 30kw pack interchangeability; that it can't be done. I have the feeling that it can and will be interchangeable WHEN Nissan decides. At this point tho, they don't want to cannibalize sales of their new cars. I sorta feel like if they can offer a last gen battery upgrade to a car that is several gens behind (30 to a 24 when the 40 comes out or 40 to a 30 when the 60 comes out) they're not really hurting their own cause and will get accolades for being "responsible" by not building a bunch of EV's that have range issues, get passed around like a hot potato near the end of their short life due to range issues.
I could see engineering the 30KW pack in the same size as the prev 24kw pack as that car had the same shell, but designing an entirely new car around the old battery pack dimensions could only mean one thing...future intentions of making it "backwards compatible."
Mark my words, it WILL happen but ONLY when it makes sense for Nissan to do so. =)