I would like to see a cultural victory condition that relates, not to condensing your culture in your own legendary cities, but to spreading your culture to the cities of other civs.
This spread could happen along trade routes, through corporations, through your religion (if it still exists in any form), across open borders, etc, etc. The spread could be hastened by the existence of airports, harbours, etc. in the targeted cities as well as your ownership of wonders such as Hollywood and the subsequent trading of the associated luxury.
This to me would represent a more sensible cultural victory as your culture infiltrates other civilizations and becomes the dominant worldwide culture.
In the real world there are many examples of this cultural seeding...a McDonalds in Delhi, Nike hats on children in Africa, Hollywood movies in China, Greek artifacts in museums worldwide, Egyptian artifacts on tour, German cars, English as a killer language, even the spread of British sports such as cricket and rugby through the Commonwealth and beyond.