I think Blueplate only is interesting.
If a track had transponders, couldn't they then just have two classes, by adding plates to restrict fuel?
Couldn't you have a series of plates and when you improved and got faster, you'd then have to put on more restriction via a smaller plate. It would make all equal to either the slowest competitor or to a standard track time. Maybe say if adults get quicker then 13 seconds they have to change to a smaller plate. And maybe if kids got quicker then 15 seconds, they have to change to a smaller plate. Everyone would be able to win and if you improved with either engine, driving, tires or setup, you'd be slowed down.
If you want more classes so more people can go home happy with a trophy, then just add more times that need to be met. If you want to go fast, join the racing for 12 second laps. If your not comfortable going that fast, join a class with 17 second laps.
You'd have forced bracket racing, where if you got too good instead of breaking out of the bracket, they just slow you down. ...