an idea (I know that is an After 1900 and possibly, something crazy):
Suppose that the European Union remains in its early stages or even it´s unsuccessful. Couldn´t Iberia make something similar to the Benelux, and with time move towards a federal state? I mean it would be more likely that the proper Benelux and Iberia could evolve to a "nation" faster without the EU (I, myself hope that is the destination of the EU, but take a long, long time)