They are proposing that their largest class be "over 150cc". This would group 200cc Vespas, 250cc Helixes, 500cc Aprilias, and 650cc Burgmans in the same class. I would think they should have a "over 150 cc to less than 500cc" class and an additional 500cc and larger class. Maybe even one more intermediate class to separate the 400cc Burgmans & Majesties from the 250cc machines. In that case, I might group the 500cc singles with the 400cc machines, and let the larger twin cylinders run together (Silverwing, Burgman 650).
The few participants last year were all under 79cc. So I suspect that the event organizers are not really mega-scooter aware. To an extent, I experienced this at Scootercade. The event organizers are still mentally living in the "Honda Helix" days, even though those scoots had dwindled to less than 40 of the 250+ scooters participating. They were still handing out Helix accessories as door prizes, their Maintenance Seminar was mostly Helix specific, etc.. It was still fun - but folks who want to run a general scooter event need to recognize the significant differences between the various classes of scooters available now. A 50cc scoot and a 650cc scoot both have their place in the scooter world, but are designed for entirely different purposes.