Srdjan raises an interesting point on the need to reform EU institution to be able to enlarge to other countries (Bulgaria and Roumania already have green light). I agree with this point, and I believe that few think that we can keep enlarging without institutional change (unless they militate for an implosion of the EU).
Euan, however, contends that we have to drop the discourse of constitutionalism, or at least we have to distinguish it from institutional reform.
I wonder. It really depends on how we understand the notion of European Constitution. I, for example, think that a material european constitution exists since long time (Cf Weiler, The Constitution of Europe, CUP). Within this framework, whenever we think about serious institutional changes, we also modify the constitutional framework.
Euan is probably thinking about a more formal, and symbolic, notion of Constitution that ultimately refers to the Constitutional Treaty. From this viewpoint, we can of course distinguish institutional changes from constitutional ones. The reason is that we do not need a constitutional treaty to change institutions that have always been modified by treaty. Fine.
But then again, there is a different problem with Euan's view of the enlargement. Euan seems to suggest that enlargement does not have anything to do with constitutionalism. Not true. Enlargemenent is supported by many Euro-minimalist, in particular British, who would want to see a very large market without any other political aspiration. Thus, if you do not associate the political discourse of constitutionalism with enlargement, the risk is to adopt a defaul interpretation of enlargement that goes back to euro-minimalism.
In my mind, enlargement and constitutionalism go hand in hand. Whether they necessitate the constitutional treaty rejected in France and Holland, is another story.