There are many instances where you have a group of entities which are specializations of a more generic entity.
At the moment this is difficult to model effectively as the choice is to create one entity with a "type" attribute and many fields which are relevant only to the type you choose. This involves lots of form work to show/hide and validate the correct set of fields. However it does have the advantage that it it is easy to create a view showing all of the different types together (although the fact that a user sees the specialized fields when creating a view is confusing).
The other alternative is to create many different entities each with the "base" set of attributes plus the ones that are specific. This makes creating views/relationships/reports very difficult.
Ideally we should be able to create a "base" entity with common attributes on it and then inherit those attributes to the specialized entities.
When creating views/reports it would be good to be able to create a list showing all of the entities together which inherit from the "base" type using the "base" set of attributes. In other words the ability to treat them the same base type for views/reports.
Obviously I realise this is a pretty big change, but it would be a very useful one.