It would add a minimum LOC in xorg-server to provide the ability to log to the syslog.
X is currently one of the last mainstream daemon which does not provide a way to log to the syslog.
Using syslog provides control over the way the logs are processed (eg. buffered writes which are nice on SSDs, destination control, ignores, log rotation).

A lot of troubleshooting guides are talking about reading /var/log/Xorg.0.log for info, so I don't think disabling the current logging system by default would be wise...

Basically, the syslog-only part of os/log.c would look like :

#define SYSLOG_NAMES
#include <syslog.h>

const char * LogInit(const char *fname, const char *backup) {
  openlog("Xorg", 0, LOG_LOCAL0);
  return "/dev/null";
}

void LogClose(void) {
  closelog();
}

void LogVWrite(int verb, const char *f, va_list args) {
  vsyslog(LOG_INFO, f, args);
}