Apart from price, would a pro be prepared to risk injuring himself in a malfunction? I'd guess a typical pro would put career above engineering glory. If the pro did it for free you'd probably still have to buy an insurance policy to cover him.

Pro cycalists already take risks; if their bike has an issue, or their path has an issue such that they fall they are potentially looking at serious injury. Not to mention the fact that prior to the test proper, the mechanism would be well tested to make sure it won't fall apart, and there would likely be many practice runs with additional safety percuasions until everyone was comftorable.

Also, how is powering the first human powers flying machine not good for a professional athlete's career?

Playing with semantics, if a pro agreed to power such a helicopter, he'd most likely be doing it as an amateur, since amateurs do things for the love of it!

Pros take risks, but I'd theorise that a part of the career would be managing those risks, to maximise the career. It would be very cool to power the first human powered helicopter, but I suspect we are not typical, in that the typical punter cares more about sport than a helicopter. From a professional point of view, the fame and returns from piloting a helicopter are negligible compared to the rewards of improving in the Tour or the Giro.

I'm descending into hot air production here, since I have no real evidence on which to base it!