Why do you state that when the article linked clearly says: "The cause of the accident was not determined, although Buckminster Fuller reported that the accident was due to the actions of another vehicle that had been following the Dymaxion closely.".

It's a pity investors bailed on the project, it seems like it was well ahead of its time, prototype failures are usually experienced behind the scenes, not in front of an audience that large and I think that they investors probably were on the money pulling out because of public perception, even if they blamed the tech, it was not the wheels that had anything to do with this, but more likely a lack of reinforcement of the main structure of the car.

As for flywheels: http://afstrinity.com/ that company (a merger of American Flywheels and Trinity Power) is probably right at the cutting edge.

Anything storing a significant amount of energy is prone to accidents, from batteries to rocks on the tops of mountains.

Flywheels are one of the few technologies that can store signficant amounts of energy and can be engineered to fail with relative grace, as opposed to say a fuel tank blowing up. Another strategy is to use many relatively small flywheels in parallel, each in their own containment vessel.

This also helps with some other engineering difficulties involving flywheels. Flywheels are ancient tech, at least 50 years old but probably much older, and if you count them as storage devices in a purely mechanical context as well then you can go back in to history quite a bit, about a thousand years.