There is a proposal around to create a merged appellation covering both entities but many people, including me, think this perverse because of the distinctiveness which Victor pointed out.
Reading RVF’s review of the 2009 vintage, I learn that this is no longer a proposal but has become a reality. Languedoc AOC covers entry level wines from the Mediterranean Spanish frontier up to, but not including (I think) Costières de Nîmes.
Initially it will co-exist with the existing appellations such Coteaux du Languedoc, Côtes de Roussillon, Faugères, Minervois, etc., but it is intended that Coteaux du Languedoc should disappear with the better areas, e.g. Montpeyroux, Pic-Saint-Loup, La Clape, acquiring appellations in their own right. I do not know what is proposed for Côtes du Roussillon or Côtes du Roussillon Villages, but I find it hard to believe that a vigneron like Gérard Gauby, who puts Catalogne Nord on his label, would have any truck with Appellation Languedoc (a bit like telling the Scots that their whisky has to be called English).
Here is a coarse translation of what RVF says about Languedoc AOC 2009 –
The appellation is very young but is already being talked about. Born in April 2007, the founders’ intention was to provide a framework for the production of quality wine. A seductive idea on paper! The results are half-hearted. It is true that the appellation is little by little finding its place in the Languedoc landscape . However the policy of thereby promoting wines which are supposed to represent the region costing between 3 and 7€ is calculated to confuse wine-lovers. Because, having set aside faults such as dilution, over-ripeness or bitter tannins, the majority of the wines of Languedoc AOC are distinguished by….their overwhelming ordinariness. Supple and easy drinking, they are made in a consensual and technological style which confirms alas! what we feared; a levelling down of the production from the Spanish frontier up to Nîmes….a worrying situation at a time when hierarchical classification in other appellations is under way.
So the subliminal message is avoid Languedoc AOC, if you want a wine of character. The French frequently shoot themselves in the foot with their appellation decisions

