The book Synthesis of Subsonic Airplane design by E. Torenbeek contains some sections on jet engine placement. According to the writer, buried engine installation was favoured by British designers and podded engines by American designers.
Figure 2-12 depicts four bomber planforms, one American and three British. The wing area of the British designs are quite large to provide the space for the engine mounting compared to the wing of the B-47, while span is identical. The book then mentions some of the advantages of wing root mounted engines:
a. The extra draq resulting from the buried engine installation is only a few percent as against about 15% of the total drag in the case of a configuration similar to the B-47. Incidentally, the current generation of turbofans show a value of about 8 to 10%.
b. As a result of the low wing loading and low value of $C_L$ in cruising flight, maneuvering is possible without compressibility problems such
c. The pitch-up problem of swept wings is less significant for low aspect ratio wings.
d. As a result of the low wing loading, the low- speed performance will be better.
e. The relatively low aspect ratio wing box structure will lead to greater stiffness and aeroelasticity will be less of a problem.
Many of these arguments are only valid up to a point, and in particular the progress in engine technoloqy towards high bypass ratio engines, together with the development of more efficient high- lift devices in 1950-1970, has settled the case in favor of high wing loadings and pod-mounted engines .
So wing root mounted engines have less drag, however wing pod mounted engines provide bending relief of the wing which saves on structural weight. When mounted in pods in front of the leading edge, they provide torsion relief for aeroelastic effects such as flutter. Less drag was the only direct advantage of having no engine pods, all other advantages cited are due to using wings with low aspect ratio/span loading.
From Torenbeek section 6.5.1
Engines buried within the fuselage can only be used when the payload has a relative1y small volume and enough space is available for the engine and its inlet and exhaust ducts and for the wing center section. Generally speaking, this will only be the case with small private aircraft and trainers, as far as civil aviation is concerned. The relatively large diameter of modern high bypass engines virtually pro- hibits the installation of engines buried in the wing roots, as in the Hawker Siddeley Comet and Tupolev 104.
So turbofans are most impractical to install in the wing root, pods underneath are really practical maintenance-wise. Perhaps ramjets, but how does the aircraft get to the speed where ramjets can operate?