I think it would be best as an evolutionary process... if/when it seems natural to do so then it should be done. Some people can be rather patriotic, and aren't going to be well pleased with such a notion, particularly if it's perceived as resulting in a loss of autonomy.
Until that time there's still economic benefits being derived from the establishment and functioning of an EU (I guess that makes sense since it was originally the European Economic Union).
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"Whether I were to preach in brief, Sāriputta, or whether I were to preach in detail, Sāriputta, or whether I were to preach both in brief or in detail, Sāriputta, rare are those who understand." (A I 333, Sāriputtasutta)