NASA is unlikely to find any use for the L3 point since it remains hidden behind the Sun at all times. The idea of a hidden "Planet-X" at the L3 point has been a popular topic in science fiction writing. The instability of Planet X's orbit (on a time scale of 150 years) didn't stop Hollywood from turning out classics like The Man from Planet X.
You can read this question's sibling question if you like, but my question here is:
Did the film The Man from Planet X (1951) refer to a planet that was (at least at one time) in an orbit similar to the earth but on the opposite side of the sun?
note: This was the case in another SF film: Journey to the Far Side of the Sun (1969).