Data Migration & Backward Compatibility Scenarios

We're changing a feature that has existing user data. Identify migration and compatibility scenarios.

CURRENT BEHAVIOR:
[How the feature works today]

NEW BEHAVIOR:
[How the feature will work after the change]

DATA CHANGES:
- [What's being added/removed/modified in the data model]

USER SEGMENTS:
- Users who have [old data type 1]
- Users who have [old data type 2]
- Users who have never used this feature

For each segment, generate:
1. What happens when they first encounter the new version
2. Acceptance criteria for the migration experience
3. Whether any data loss or behavior change is visible to them
4. Rollback scenario (what if we need to revert)