Is there any documentation on the macOS Sierra new logging system?
Most of the logging that was being redirected into custom log files has defaulted back to the system log. As was mentioned in the post you referenced, the log command (man log) is the best way to access the information. 

For netboot issues, looking at log messages from bootpd &amp; tftp should give you useful info.

log stream --predicate  '(process == "bootpd") || (process == "tftp")' -info