I recently read up where a flywheel shattered at 5700RPM
Yup, and some folks have been abducted and probed by aliens. It must be true because I read it somewhere. Believe nothing of what you hear and...you know the rest.
Only once have I witnessed a flywheel explosion. It was because flywheel was heavily modified and was then able to reach/pass its
terminal rpm. Could also have been due to improper torquing.
An ungoverned engine running at full speed
and no load is much more dangerous than the same engine
with a load.
Loneagle will not have a problem. He will never achieve red line rpms with his application, governed or not. Same goes for most engines out there.