The Comet design with the engines buried in the wings was OK for turbojets or early generation turbofans, because of the low bypass ratios and smaller diameter of those engines.
However, newer turbofans have larger bypass rations, larger diameters, and therefore btter specific fuel consumption. The Comet design cannot accomodate up to date engines for aircraft in the B737 or Airbus A319-20 category.
Compare the engine bypass ratios and advertised unefueled ranges of the P-8 to the NImrod MR-whichever.