A lot of the need for this design is for backwards compatibility with existing corporate network designs that will likely be on IPv4 for perhaps another decade

A lot of the need for this design is for backwards compatibility with existing corporate network designs that will likely be on IPv4 for perhaps another decade or two longer. Most corporate networks despise changes and seek to gain stability of their environment through minimizing changes. My current contract customer absolutely wants this and requires it, in fact, for compliance with internal security policies (nevermind the litany of security issues using IPv4 in the first place). The limitations of this solution include the fact that we're unable to get much control of these instances because we use third party software galore on these type of NAT instances like IDS, firewalling, caching / proxying, and traffic shaping. So unfortunately, all this new service does for us is let us separate out one of like 12 functions to a (granted, high availability) service and in the interest of saving money on not creating 25+ instances for these 12 services it's not unheard of to collapse these into 3-4 load balanced / distributed much larger instances for the sake of easier manageability. But for a lot of folks, I can imagine this is a great service that meets their needs sufficiently well.