To my knowledge, Nissan is on a 6 year refresh cycle with the LEAF. What I'm not sure about is when they started counting. Is the first gen LEAF MY11 through MY16 (I guess it is)?
So, I think that means the second gen LEAF starts MY17, coming out late 2016 (guess on my part)?
But what is interesting in the mean time are hints from Nissan and their pattern of mid model refreshes in other models. I don't expect a body change (too expensive for a relatively low volume car for only cosmetic changes), but I am wondering if we'll see the appearance of either the new NMC battery chemistry or another beefier improvement. I (personally) wouldn't be surprised to see a 36kWh battery for MY15, but this is complete conjecture on my part. I think Nissan knows it needs to up the ante before the second gen and with the hints we've been given this fits right in.
I would also not be surprised by an option for a second pack in a second gen LEAF, depending on battery prices by 2017. But again, complete conjecture.