I bought a 2017 last month knowing that LCI was coming. The tweaks they applied to the 2018 weren't enough for me to hold off because I want the car NOW.
My advice - use the coming 2018 to press for a discount on any remaining inventory on lots. And yes - there is inventory out there. I found three cars in 48 hours when I searched last month. Ended up in NOLA for my purchase and got a $4K discount (including the USAA)