You don't have to explain the perils of extending L2 over any type of WAN to me. There used to be a hard requirement from some SANs to have dark fiber for their replication - not just L2 adjacency (needed actual FC zones extended to another site if I recall). But all is not happy times with L3 links and BGP between things (and even then, BGP configs to achieve anything decent in terms of failover needs BFD or more). But sure, poop all over this fun thought experiment if you want, I doubt anyone's going to deploy this and put a billion dollar company at risk.