Just a word about the "spaces" for deceased kings at El Escorial. It is true that only one sarcophagus remains empty and it is designated for the former Queen Victoria Eugenia wife of King Alfonso XIII. A guide told us something about places to be created for the Count and Contess of Barcelona (parents of the present King) above the doorway of the Royal Pantheon. The reason for the delay in the final disposition of the bodies is that only bones are placed in the "caskets" after 40 years of "rotting" and decomposition. Sorry, folks. The Kings are on one side of the crypt, and the Queens on the opposite side, but they are only included if they were a mother of a King.
The present King and Queen have never mentioned anything about burial plans. I guess they don't want to think about it. It is a big mystery!