Probably never. ESXi is designed to be stripped down and does not support much in the way of management outside VC and the VI Client. You can post a "feature request" in the Feature Request forum, but you're not likely to get a response from anyone at VMware on the issue.
Because ESXi administrators couldn't possibly want to do statistics gathering over the life of the server in their enterprise tools (such as Zabbix, or Nagios, or MRTG, or Cricket, or Cacti, name your poison).
That actually might be enough to make me stick with ESX "standalone".