From what is publically available, LEAF/Next will be announced on September 5th 2017 in the US, and info on the specifications and a pre-order site will also be up that day. In the weeks immedialtely after the announcement there will be events across the US where you will be able to see, sit, drive and pre-order the car, with the first customer delieries beginning in December for those that pre-ordered. I suspect that dealer inventory will begin to flesh out in the January-March '18 time frame, but it appears that pre-orders will get priority.
2018 LEAF SL
Delivery April 10 2018
2014 LEAF SV
Delivery May 23 2014
50,000+ miles - all 12 bars - Same range as new - No warranty issues ever!