20-Year Prospect
Rugby's a growing sport that's been around for a solid hundred-plus years in Europe and shows no sign of dying out. Once upon a time, it was a fairly popular sport in America, and there's no reason it couldn't one day be there again (source).
If anything, with the reinstatement of the sport in the Olympics at Rio 2016, U.S. rugby stands a chance of one day changing people's minds that it's worthy of a having an actual professional, multi-city American league. Maybe in twenty years, after a few rounds at the Summer Olympics, it'll finally get off the ground.
The sport itself may end up changing in subtle ways as well. As more research is done to figure out the relationship between concussions and other head injuries and long-term brain health, more safety precautions may find their way into the game. We're not saying anyone's going to have to wear helmets or anything, though. That's just crazy talk.