It's because Cisco didn't test iSCSI. Cisco's internal support policy goes something to the effect of "If the BU didn't test that exact scenario, TAC doesn't have to support it."
None of us will be able to comment in a public forum of what may or may not be added in the future. All we can do is talk to what is publiclly documented. The Unity Virtualization document specifies Fibre Channel. The best direction you can get is what Cisco is doing more recently for virtualization. All of that requires FC or FCoE as well though; no iSCSI love.