A well known rider was killed a couple of years and the unofficial cause was that the engine had done to many miles and advice from the tuner was ignored.
The Americans have the right idea in 600 racing and thats formular extreme, and the parts/spares to build these bikes are readilly available, so why not listen to an expert and go down the same path. The TT is unlike any other race so should have its own rules and made with the advice of those that know what they are doing and not by those that dont, full stop.
What would happen if a rider was killed on an illegal bike and his family took legal action agaist those that built it.