It's potentially a problem. I believe the thinking is that a single OD class may end up putting more kids into cats in total than the sum of those that might otherwise take to a number of smaller independent classes - due to the benefits of global critical mass. The attractiveness of a particular boat for racing is related to the number of other people for you to race against. Coalescing around a single design is more likely to generate sizable fleets that will attract more and more sailors.