Work on this request has commenced. We will send an update once it is completed.Todd Cotten commented
This is definitely an important feature for anyone doing reusable arm templates. Take data disks in an IAAS VM as an example. If you are using a VM copy loop to say create some web servers that may or may not need data disks there really isn't a way to accomplish this cleanly without getting into non-resource creating linked templates with references to outputs or managing two VM resources that are almost exactly the same. You can't use conditions on property copy loops which frankly is just a Band-Aid for this feature anyway. Variable copy loops don't have access to the VM copy loops index and functions can't implement loops at this time.
136 votesunder review · AdminAzure IaaS Engineering Team (Azure IaaS Engineering Team, Microsoft, Microsoft Azure) responded
This is something that we are reviewing to determine when we can support the functionality.