I don't really see the point of this. It's implemented as a protocol, and thus the bottom of the qemu protocol stack. So we might get SCSI commands in from the guest, decode them, just to re-encode them again and send them off to the network all inside qemu.
Do you have any performance numbers showing why the addition of the code is nessecary over just using the kernel iscsi initiator? Which btw, is a lot more flexible as it also supports SG_IO passthrough and thus accessing other devices not supporting the SBC command set.