Existing Wording: In order to make the use of extensions safe and manageable, there is a strict governance applied to the definition and use of extensions. Though any implementer is allowed to define and use extensions, there is a set of requirements that must be met as part of their use and definition.

Comment:

Although there is strict governance on how to define extension, it is still likely that extensions may be added in incorrect manner say as part of wrong resource (essentially modeling or relationship issue). There will need to be some process and guidance around how to and where to add extensions to make sure the extension can retain the purpose and meaning of the resource it is added to. Without such guidance, it could result in lot of extensions added for specific interfaces that may continue to be bigger problem over time and result in interoperablity issues in various contexts.