You might be right. Not sure if he is the kind player Guardiola would be looking for? One thing is for sure, there are English clubs that are able to pay him more than the salary Chelsea offered him. In Germany there is probably only Bayern and Dortmund, so you might be right and Spain could be his next destination.
I actually said that as players usually in order to show respect to the club opts to move to other league instead of teams in same league. Having won the CL with Chelsea, Rudiger simply doesn't falls to me as a guy who will just make a move to English club in PL. Spain, Paris , Italy, Germany...lot of options for him.