Sorry for the late reply - hopefully you've asked elsewhere and gotten better responses. I'll share what we've gone through and where we see SCCA going. My son started with the JC kart and Comer C50 his first year, then moved to a Comer K80 in JB the next year. Talk about under-powered and finicky. We switched mid-season to the KT100 and once I figured out the little carb, it ran great for a few years. By this time I had joined the KAC and learned that the SEB was pushing us to adopt the World Formula as a spec motor for the JB and JA classes. The karting parents didn't like that idea, but the SEB didn't want to let it go, so a compromise of sorts was adopted: make the World Formula a favored motor by weight differences between it and every other motor. It quickly became clear to most karting parents that the WF was the chosen motor under this scheme and satisfied the SEB by performing an almost wholesale switch to the WF over a few years.
While I resisted the switch initially, we did go to the WF a few years ago and I can honestly say that we both couldn't be happier. Once we worked out the kinks in the tuning and got his corner-balancing better, it's been a great switch. The motor weights 2x the KT100 and with smaller kids like my son balancing the kart can be challenging. But it's as close to a "set it and forget it" motor you'll find - very little adjustment and tuning is required to get it in its broad sweet spot. And no more external starter to worry about charging and carrying.
While we are adjusting weights again, the WF is still going to be favored to make it the de facto standard. I don't see that changing.