Since Cannonlake is finally out, it can be called a milestone. Once parts are out, things often improve rather rapidly. The Y part, 8114Y isn't here yet but computex is a reasonable expectation. That means that could be the earliest launch for Icelake. The better scenario would have been if CNL-Y was either earlier or skipped to hasten Icelake Y but it doesn't seem to be the case. Mistakes can't be skipped, it has to be something to learn from.
To keep with the fluidness of Intel roadmaps, I expect:
-Icelake-S, a year after CFL 8C, or BTS 2019
-Icelake-Y, a year after CNL-Y, or likely Computex 2019
-Icelake-U 15W, a year after Whiskeylake-U, or BTS 2019
-Server isn't as clear, because we don't know if Cascade Lake will launch early and do a separate Intel DIMM support in Q4, or just wait until Q4 for everything. I think a staggered launch is possible.
Interestingly then, that leaves Coffeelake-U 28W/H as the lineup that can be replaced earliest by Icelake in Apr/May. If they want to do a limited low volume launch, they can wait for H chips later and only release Icelake-U as a 28W part.