Will we ever see a single-engined airliner? Given the trend in the industry to move towards aircraft with two engines, could it ever occur that we see an aircraft manufacturer develop an airliner with just one?

I'm suspecting the answer is no, given the redundancy offered by a twin engine configuration (e.g. if the independent probability of engine failure is one chance in a thousand, the probability of dual engine failure is one in a million.). I know the Virgin Global Flyer used one engine (https://en.wikipedia.org/wiki/Virgin_Atlantic_GlobalFlyer) presumably because the risk of engine failure was acceptable given the task in question.

However, if someone were to manufacture an engine with a probability of failure below, say one in 100 million, could this configuration make sense from an economic perspective?
There are two major problems I see.


Even if you have an incredibly reliable engine how do you prove it is incredibly reliable. I can't seem to find figures for the target IFSD rate for the current higher ETOPs levels, but I find figures for early ETOPs of one per one hundred thousand hours. Lets say you improve that to one per billion hours, how exactly do you demonstrate it's that low? fly for a billion hours? Thats a hundred planes flying for a thousand years. This is why redundancy is the route taken for many safety critical systems, you can argue that the individual components are merely very reliable and then argue that the chance of two of them failing at once is extremely low
Where do you put the engine? If you have a single engine you want it on the centerline. That is not such a problem for props or low bypass turbofans, but it's difficult for high bypass turbofans.


Because of these two factors I doubt we will see airliners move to a single engine configuration unless we see fundamental changes in airliner design and regulation.