Conclusion
A survey was conducted to determine whether the Gerrit community would have concerns, if case insensitive username handling would be made mandatory. One third of the respondents voted against the feature being mandatory, mostly because the use case sensitive identity providers. Cutting off that many users from updating is not desired. Thus, it was decided to make this feature optional. However, for new sites this case insensitive username handling will be enabled by default.
Online migration of external ID notes is a desired feature to allow zero-downtime upgrades and will be implemented at a later point in time.