Autocompletion does work for M2O in editable list when modifying an existing value
When the user change an existing value of a M2O field in an editable list the autocompletion search for this field is not triggered.
This is due to the fact that the underlying value in the field is set thus the call to _update_completion does not make the call. This process works for M2O fields in the form view because we're catching the changed signal and resetting the value of the underlying field.
The attached review adds the "changed" signal mechanism to GenericText and implements a simple version of it for M2O fields.