Lots of EBS volumes mounted via 25GBPs or higher network, positioned carefully onto a single rack where possible and carefully tuned network/ip/os for both clients and servers. It is not feasible in most deployments as this would not have scaled to real production loads (RAID configurations requiring redundancy alone would slow you down, not to mention costs of using that many EBS volumes on extra high network/IO/provisioned IOPS nodes). This was only meant to prove what was possible in AWS at the time.

Not in 2015. 25GBps didn't even arrive until 2016, and dedicated EBS bandwidth didn't arrive until 2017.