After some research can now answer my own question. The road is actually A19 not A79 and was formally opened on 6th June this year. If you are going from, say, Chartres or Le Mans to Dijon or futher south east, then it appears to save wandering through the smaller roads in the area north east of Orleans.
Beware that routes from ViaMichelin, Mappy, AA etc. do not show this road whereas those from the french site Bison Fute do.