Consider the scenario originally described at #9213 (comment) (about why instance functions on DbContext can be compelling):

db.Posts.Where(p => db.PostReadCount(p.Id) > 5);

It could actually be even more compelling to be able to do this:

db.Posts.Where(p => p.ReadCount() > 5);

This could work for instance methods, computed properties or even extension method defined over the entity type.

It would be convenient for the translation to automatically map the "this" entity instance to the key of the entity when invoking the database implementation of the function.