I think it would make a good enhancement if we can use custom keywords. So similar to writing custom Java services, actions, etc, if would be really handy if you could define a keyword. A keyword which returns the current week number, the name of the latest entry added, a date in a specific format, that sort of thing.
Imagine you have a record grid where users can create a schedule based on week numbers. Ideally the field should have the current week number as the default but that's currently not possible. But if I can somehow define a custom keyword I can just use this and set it that way.