I would greatly benefit if the "allowed hosts" item field would also be subject to macro expansion. This would add a little more security to templated zabbix trapper items, where the remote host will submit measurements by means of zabbix_sender.

Currently that's not supported:
https://www.zabbix.com/documentation/2.0/manual/appendix/macros/supported_by_location#macros_used_in_low-level_discovery

Thanks for considering this feature.