I have an idea to solve this problem https://www.zabbix.com/forum/showthread.php?p=147817
If we can "tag" an interface like "WAN" in host configuration page, items on template can be assign only to interface named "WAN".
For example, I have one host, a pfsense with 3 interfaces, WAN, LAN, DMZ. I create this host and assign my ips to the interfaces (192.168.1.1 -> LAN, 95.x.x.x -> WAN, 192.168.2.1 ->DMZ).
So my template has 3 items named icmpping[LAN], icmpping[WAN],icmpping[DMZ] and all are checked on my host.

I know, I can use user macro to approach this functionality, but it's not easy for the user. IPs in "agent interfaces" are no sense if the user want use only template (and not item directly on host). Moreover, IPs are duplicate (and not linked !) between macros and IPs configuration.
Save the host can check if interface name correspond to the template items, if no one interface is named "WAN" and the host is linked with a template whose had an "item's WAN", the host can be saved.

I think it's a good feature for many users who want to check all (or more than one) interfaces on a host using host configuration (and not user macros...)