Host Groups to support Inventory, Host Group Macro

It would be great if we could apply either user macros or inventory items at the Host Group level. This furthers Zabbix's use as a CMDB, and greatly improves the ability to customise all aspects of monitoring (enables monitoring of host groups as an object).

My specific use case is that I discover hosts via Autoregistration or Network Discovery, however have no way of automatically inserting a host inventory item saying that this host is part of "Host Group 1". The only way I can currently obtain that information is via host.get via API, or by inserting an inventory value via API (for example, site_address_a get's the host.get selectGroups value).