First, no economist that I know of, either on or off the Sarkozy Commission, has advocated ditching GDP. What’s under discussion is the possibility of developing good supplements to it.
Second, the viability of economic accounting measures is not completely determined by the ability of existing data. Once we decide something is important, we can figure out how measure it. Data are (at least partially) endogenous!
The first point is right–it’s the non-economists (such as Sarkozy) who speak of actually replacing GDP. And as for the second, well, this is why we need to Save the American Time Use Survey!