The use-case for us is a trigger defined to detect a mismatch between the hostname reported by the Zabbix agent and the actual Zabbix host definition.

Detecting this helps us when there is a misconfiguration preventing the Zabbix agent retrieving its active checks from the Zabbix Server and/or Zabbix Proxies.

At this point we use a {$USER_MACRO} which is allowed, however it would be useful to allow the {HOST.*} series of in-built macros to be used in both Trigger expressions and Trigger recoveries.