I've heard they basically canceled Cannon Lake for desktop in favor of pushing up the Ice Lake launch, so Cannon lake will be mobile only.
Intel has really fallen behind on their release schedule due to how much trouble 10nm has given them, so now they are trying to push product lines through. Remember Coffee Lake wasn't originally a thing, we were supposed to get Kaby Lake then move to Cannon Lake then Ice Lake, but they had to introduce Coffee Lake as a stopgap, and aren't keen on delaying Ice Lake.