I cannot see anything in the log that would explain why the serial console driver didn't provide any output on the Debian kernel 4.13 (with the devicetree from 4.14). Would you perhaps be willing to do another test run once the debian-installer has moved to kernel 4.14?
Yes of course, only how can I tell that the installer is using 4.14? Invoking "file" on the image doesn't tell me the version how it usually does.