As part of the gradebook push 2014, we're developing a new date and time filter on all grade export formats.
The main concept is allow users to export grades from a past date to now, and save the last export date for further reference.
Another benefit of this new feature would be standardize all export formats (OpenDocument, Plain Text, Excel and XML).
We're still considering about the possibility of replace the *Export new or updated grades only* by this date filter.
However this could be expensive because the XML structure is different of other export formats and is being used by OU and it rely on a config: *gradeexport*.
Link to the issue: https://tracker.moodle.org/browse/MDL-47022
Comments, ideas, suggestions and critics are always welcome.