The Core program currently does not support adding master editions to collections. This is problematic for creators who have been used to organizing both 1/1 nfts with editions in the same collection using the Token Metadata program.
We propose adding a new Group account type that is similar to the Collection account type, but does not need to support plugins. Users should be able to add both Assets and Collections to a Group, which will allow 1/1 nfts and master editions to be organized together. The same authority validations should apply when managing items in a Group as they do for Collections.
Furthermore, the DAS api should be updated to handle querying by Group address similar to how it works for Collections.