"Copper oxides, also known as cuprates, are the most promising materials for superconductivity. Today, cuprates can be superconductive at temperatures as high as -150 °C. But for many years scientists wondered why they lose superconductivity when concentration of electrons drops below certain level. Most scientist thought that the cuprates gradually became insulators.
Scientists from Université de Sherbrooke discovered that the loss of superconductivity is because of a sudden appearance of a distinct electronic phase in the material that enters into competition with the superconductivity and weakens it. It means, that higher temperature superconductors will be possible if we can get rid of the competing phase. This new approach opens a way to get an ambient temperature superconductivity."
To be fair, I think it was only Williams who used a flywheel and they ended up giving up on it and swapping to a battery-based system, but the point remains that a Formula One team, who employ some of the best engineers in the world, let alone in motorsports, spent a year or more experimenting with a flywheel-based energy recovery system, including development along with testing and the races they used it in -- which says quite a bit.
Yep, catastrophic failure can be well, pretty catastrophic, especially with those type of flywheels.