The Ice Lake and Cannon Lake CPUs are ultra-low voltage processors featuring the 10 nm manufacturing process. The Coffee Lake-U i7-8559U CPU seems to be similar to the existing Kaby Lake-U CPUs, but its specs have been bumped considerably.
https://www.notebookcheck.net/New-Intel-Ice-Lake-U-Cannon-Lake-Y-Coffee-Lake-U-CPUs-and-specs-get-leaked-on-3DMark.286776.0.html
Your prediction of 28W may be right. I suppose that chip will be in the upcoming Bean Canyon NUC.