As mattdm notes, rangefinders use a focusing mechanism based on parallax. Several opine that any popularity rangefinders might have had were for their compact size, not their focusing mechanism. (mattdm, Hueco, Crowley)
However, there is at least enough demand for Leica to continue making and selling rangefinders for a huge premium, despite their relatively low volume. The true level of demand and the price the market would bear is unknown because Leica has a monopoly on digital rangefinders.
The popularity of rangefinder-style cameras, made by Olympus, FujiFilm, and others, demonstrate that there is demand for the rangefinder look, for which people are willing to pay a modest premium. These cameras are externally modeled upon classic rangefinder cameras, but use autofocus and TTL technologies. If a rangefinder focusing aid were added to one of these cameras at a reasonable price, it would attract those who are fond of true rangefinders.