I understand that a single indicator can be useful, if only for communication purposes. However, any composite index will need many choices about what to include and how to wheigh them. And given that there is no more or less "natural" choice for these weights (as opposed to for example the weights used in stock market indices),
it is going to be vulnerable to tuning to get desirable answers.

To put it bluntly, I can't imagine the EU developing an index on which it (or at least its richer parts) score below the US, nor one on which Germany and France differ substantially from each other, or score below the UK. In fact, I don't think the UK will adopt any measure developed  by the EU, no matter how well it scores on it. Basically, if the EU as organization is involved in its development, no matter how good the measure is, it will be a bit suspect

I think it would be much safer if separate people, countries and organizations develop their own measures for their own purposes, much like the CIW you mention. Then, after these have been tested and fine-tuned we can compare them, see how they correlate and scale to different countries and situations. After that, the politicians can come in and pick one that works as they would like it. Let them pick a car but not design the engine.

Perhaps I am mistaken, but this conference seems to be about a much earlier stage in the development. It would be wise to let them explain what they would like to see in an index, but please let independent people develop the details.