In the 90's we were trying to get engines to rev over 10,000rpm. There were still crashes then but not as many serious ones that we are experiencing now. Todays engine can achieve 18000RPM but is restricted to 13500RPM. I'd have to ask the question why would an engine tuner build a motor that cannot be used to its full potential.
For me the bore size should be limited which would mean a longer stroke to get to 500cc & in turn this would reduce the RPM to a usable level.
The short stroke engine has not made the sport any faster as the list of track records will support only a fraction of a second each time it is reset in most cases & less than a second over a 25 year spread.
The short stroke motor has made the sport more about who can hold on the longest & who is prepared to take the biggest risk rather than the best control & skill set