Why iSCSI?
-because every comparable NAS solution already has it (FreeNAS, Synology, Qnap, OpenFiler...),
-because it is easy to add,
-because it would help some of us, already using unRAID for everything else, dump other solutions existing for the sole purpose of serving iSCSI targets (think mostly for ESXi home labs),
-a few other edge cases where access to block-level devices is required or preferred over smb or NFS.
On the other note I don't get why some people uninterested in the topic try to discourage Tom from looking at it. I don't have any use for e.g. graphics card pass-through to VM, but I don't advocate to stop wasting development time on it.