What about a feature to move fields from one entity to another? Use case example -- fields were created on nodes using content profile in D6, I want to move them to either the user or a Profile 2 entity in D7. The field data is migrated fine and ends up on a D7 node, just need a way to switch the entity the fields are associated to (see http://drupal.org/node/560324#comment-4817254).
Another use case -- I have a bunch of populated image nodes and now would like to use media module and move the field data to a media entity from a node entity.
No code to provide at this point, but it should be possible.