I think having a bin/pg_logparse tool that can parse postgres' config file and attempt to parse the log contents in whatever format they are would be much much more useful. Obviously not every log_line_prefix can be parsed unambiguously, but a lot of formats can, and a lot more formats can be made unambiguous (e.g. adding escape logic to application name logging would be very useful).
Aren't application names set by the client? If they are currently logged without escaping, couldn't a client insert arbitrary binary content such as terminal control sequences into log files, with potentially unpleasant results? Or is there some sort of filter already in place somewhere? Should I investigate?