Vienna is nice, but also a has-been much like Rome or Athens is. Not just in raw power, but in intellectual capacity - its best minds are gone, or possibly underutilized and working some boring jobs. But given the Holocaust, I would bet on "mostly gone". (Same with Budapest, BTW. There won't be any new Jewish-Hungarian "Martians" like von Neumann or Teller.)

The only pre-WWI European capital that remained truly globally relevant is London.

Istanbul and St. Peterburg are also important megacities, though stripped of their capital status.