I wonder if the technology churn is more of an issue with the structure and organisation of GOV.UK rather than a technical one. In the post he states that the previous router was unmaintainable as there was no-one with a deep knowledge of Scala in the team and that this was the main reason for the re-write. Why was this allowed to happen? Is there a rapid/high turn over of staff or are teams moved around without regard for skill balance?