I dreamed that you updated this. So do it.
I think that Alfonso X of Castile was a serious candidate in his time. His plan of being crowned by the Pope failed, though.
You're right, but not in this time. Alfonso X lived in the XIIIth Century. And he tried to become Emperor, but he was not even crowned King of Romans, which was achieved by Richard of Cornwall, who however was never crowned Emperor. Actually, no one was crowned emperor since the death of Freidrich II for over 100 years.
Take care!