In those days you were nervous about crossing oceans with less than 3 engines but then we all started getting flights to Florida on 757s and even smaller aircraft. BA use an A319 for business class to JFK. If the price is right I suspect passengers would turn a blind eye to a further leap of faith.
That said, I'm not sure Single Engine Airliner would be good for routes over risky terrain. Once you get lengthy 'ETOPS' requirements then your second engine needs to be so good (reliable and efficient) you might as well promote it back into a twin configuration. It's more the London-Paris, Frankfurt-Malaga, New York- Miami etc that could produce savings.