- #1977498: Add version tracking for configuration schema and data list some (but probably not all) of the problems with changing a config schema once other modules have come to rely on a particular state/version of it.
- Fixing that issue (in the sense of adding config schema version tracking into core's APIs) has been postponed to 8.1 or later.
- That means core will need to be very careful about any config structure changes it needs to make between 8.0.0 and whenever that issue is fixed.
- But what about contrib? Can a contrib module make changes during its alpha or beta releases, like Drupal core has done many times during its alphas and betas? Can a contrib module make changes between its 8.x-1.x and 8.x-2.x versions? If it does make such changes, what does it need to do and/or what do other modules that provide default config for it, implement potential overrides for it (such as via Domain module), etc. need to do?
Discuss. Figure out. Document.
User interface changes
Data model changes