I think significant resistance would come more in nationalist tones, than for practical reasons. For Belgium, France, Spain, Poland or Italy, the first-level NUTS regions would more or less correspond to the current sub-national EP election regions -- only the number of seats contested would change. For Germany, the NUTS regions are the federal states, thus the new system would bring it closer to what they have in federal elections -- also, much to the liking of the regionally strong CSU, I suppose. (Though, 18 million strong Northrhine-Westphalia still stands out -- the most populous NUTS area, unless I missed one of the Italian ones.) Many of the small countries are a single NUTS area, so again a potential change only in number of seats only. It would make a significant difference in the mid-sized countries, from Sweden to Romania (minus Belgium).

_{*Lunatic*, n.
One whose delusions are out of fashion.}