The best example I can think of are the Turtle Traders. Yes, their chosen markets are very diverse but still, currencies are part of it. I don't see any reason on sticking to just one market.
In addition, have you checked all of the people on the Forbes list? I'm sure there are a few who have traded currencies. I don't think they stick to only one source of income, right? That's not how rich people operates.
Trading is a marathon, not a sprint.