With PR https://github.com/ezsystems/ezpublish-kernel/pull/1045 ancestor UserGroups ids for the Content owner are indexed and criterion visitor for GROUP target is implemented.
With this we will need to reindex owner user Content when:
- Additional Location for owner user is added
- User Location (or subtree) is moved
- Parent user Location is swapped
- possibly more...
We also lack SPI to do implement some of those properly. UserService handles this problem by relying on search, but search should not be used in indexing slots as indexing is asynchronous.