While the concept clearly works, it does assume that current cowl technology only provides extra weight and drag, which is clearly not the case. Cowls also provide a degree of protection against ice shedding and blade separation too.
The theory of operation is similar to venturi systems where a high pressure fast moving central stream causes a lower pressure boundary at its edge which sucks in surrounding air which is then accelerated. This serves to create a duct that confines the central jet and improves efficiency while mitigating noise travelling sideways out of the stream.