I have serious doubts about a post-Medieval pod that could leave a consolidated HRE, much less one ruled from Spain.
There is a reason Phillip II didn't get his father's HRE title, managing a massive transatlantic empire and the clusterf**k that was early modern Germany at the same time in an era when communication between the two took weeks at best was nigh-impossible.
Now as for the second option, I could see some kind of romantic roman movement in architecture and art and what not taking hold. And I guess if somehow the Austrian Hapsburgs went prostetant or someone else protestant manages to make themselves emperor the pope might just crown the Spainish king Roman Emperor to spite them. Don't expect any symbolism beyond what the otl HRE or very late Byzantines used though. People tend to not turn themselves into walking anachronisms on purpose.