Looking forward, the findings as well as the methods presented in this work should be very useful for providing a better understanding of the exciton-polariton motional narrowing effect . A direct generalization of the current model could be extending it to 2D with many cavity modes from the full dispersion curve , which is then referred to as the generalized Holstein-Tavis-Cummings (GHTC) model and would be the closest to experimental reality . A detailed study on the effect of the full cavity dispersion band and dimensionality will be extremely valuable. On the other hand, realistic system-bath interactions are usually described by complicated spectral density functions. For example, the super-Ohmic spectral density is usually adopted for the CdSe nanoplatelet systems . To overcome the computational difficulties, the mixed-quantumclassical (MQC) dynamics methods could be potentially very useful. Last but not least, the polariton linewidth at general detuned cases needs to be derived basing on the first principle. For instance, using the Green's function method , in which polariton multiple scatterings shall be carefully evaluated in order to obtain their contributions to the polariton linewidth. These remain to be the future work.