virtio-scsi going to be really a cool implementation on virtio stream. Indeed virtio-blk was arranging that position. How-ever virtio-blk lagged/skipped lots of scsi command ioctls which paved the way to virtio-scsi. Along with virtio-scsi implementation, other downsides of virtio-blk have been lifted, for ex: the number of disk limitation..etc.. To know more about virtio-scsi, I would like to ask you to go through below urls.
A better start would be watching a demo from the people behind it.. Slides of this doc can be found at:
Also refer below urls.