I suggest a new sub-type for host interface: failover. Applicable to all current interface types (Agent, SNMP, JMX, IPMI). 

Should be added by a new button near the existing interface. After failover interface addition the first interface is marked as Priority, added - as Failover. Priority interface marker must be a radio button.

Switchover is executed when interface is marked red (unavailable) for current host. Then Zabbix should check failover ip/dns availability and automatically set all host items from Priority interface to Failover (if available). Every 5 minutes availability check for Priority interface should be performed to switch back, when it becomes available.

If both Priority and Failover interfaces are unavailable, checks must be performed for both, on regular basis.