I'd agree that packet loss is generally zero. But dirty fiber, bad ports, bad device, congestion, etc are pretty dang frequent in a large deployment. And those "edge cases" are the ones that are going to kill your poor network block iops.

I do agree on the "why tcp?" point. Funnily everyone is running the other way and wrapping up IP inside another abstraction layer. Nvgre vxlan etc are slipping yet another complication under your "simple" block device.