High-end cruise line Viking (VIK) is riding a grey wave. The California-based firm has filed to go public in New York, at a potential price of $10.8 billion, higher in relative valuation terms than its much larger peers Carnival (CCL) and Royal Caribbean (RCL). In its favor is a reliance on older, richer customers. That is fuel for rapid growth, though investors will be subject to the whims of the fortunate few, in more ways than one. Viking is not shy about targeting a fairly narrow demographic for its fleet of nearly 100 boats.