One last thought. You can use an aggregate query to do your sort and align the data scope, then use the results of the aggregate as the filter for you main model. This won’t help with the UI, but it will at least get you an ordered list back that aligns to the data.
For example, you could run an aggregate query on the Child_Relation__c table, aggregate by the ParentId and order by the Max(Date__c). Then your interactive model would be filtered by field from another model and use the aggregate query results.
