**All** of the operations in aviation are predicated on a certain level of acceptable risk, with some operations considered acceptable at higher probabilities of a failure, accident, injury or death. This extends not just to individual risks per part or manner of operation but also the sum of all those risks. The level of risk is ultimately limited by how many $$$ is considered reasonable to throw at the problem.
If/when someone makes an engine & its ancillary installation that has the same or better level of risk as whatever is the (future) current acceptable multi engined level of risk then single engine ops will happen.
No different to the IFR & night single engine turbine vs light piston twin approvals that's happened/happening in the USA, Australia, New Zealand, Switzerland and other parts of the world.