Here is collection of some ideas about possibility of running Zabbix server in a "federated cloud" of the servers, where each server can reference the data items located on other Zabbix servers, which shall be configured to work together.

At this point, it is constantly "work in progress" for this feature, but it is open for the comments.

SPEC is located here: http://www.zabbix.org/wiki/Docs/specs/ZBXNEXT-2963

UPD: snapshot from the "Wayback machine": http://web.archive.org/web/20170708230336/http://www.zabbix.org/wiki/Docs/specs/ZBXNEXT-2963