The limit has really started to hit due to the high availability of 10 gigabit and faster network cards coming down in price.
10G coming down in price? We're starting to get 40G pretty commonly now. I think the cards can be had for around 1k or less. Hell I wouldn't be surprised if we start seeing some 100G or a weird intermediate speed. With RoCE Ethernet is starting to be a viable alternative for MPI/RDMA instead of Infiniband and 40G switchports are amazingly cheap and can be broken into 4x10G interfaces to support legacy 10G server
"It ain't over until it's over." -- Casey Stengel