I think the only royal-royal marriages in the future will be Elisabeth of Belgium, Wenzel and Marie Caroline Liechtenstein and the children of Paul and Eilika Habsburg (Karoly-Konstantin is an Adonis!, maybe someone can post a photo, he turned 20 in July and loves horses)
I predict that Christian Denmark won' t marry a Danish woman and Amalia Netherlands won' t marry a man from the Netherlands.
All the others (Spain, the Scandinavians, Portugal, Japan f.i.) will marry commoners from their own countries.