We run them in the Batavia Kart Club, which runs at Avon, Cherry Valley, Pitt, and Bliss International. I’m pretty sure there’s no WF class at OVRP. I’m not sure about further east than that. We actually run them side by side with Yamaha 4-hole can at the same weight.
You can tell by the enthusiasm of NHKA racers (even ones from other classes!) World Formulas really are great. I’m surprised more clubs don’t offer it. In just a couple years it has become the one of our main entry points for new drivers, and one of the largest, most competitive classes.
I’d really love to see it get wider attention as well. The only thing I can think of is that it’s nearly non-existent at the regional and national levels and racers would prefer to run something they can compete at that level with. It’s a shame too, it’s a great package.