Coffee Lake won't launch in 2017, but I suspect it will ship at the end of 2017 so that it can launch in January/February of 2018.
Look, this thing taped out in November-ish according to a forum member here, and it usually takes about a year from tape-out to qualification for sale. So assuming no "oopsies" Coffee Lake should qualify for sale in November 2017-ish and make it onto shelves in early 2018.
Q3-Q4 2018 launch would mean that somebody dun messed up. And given how "low risk" this project seems to be (Kaby Lake with a few more cores and maybe some more L3$), Intel would have to be real bad at its job to see such a delay.