Development of active matrix imagers fabricated on plastic substrates has become increasingly possible due to widespread efforts to develop the means to create inexpensive, very large area, flexible displays. In addition to benefits associated with cost, robustness, and weight, such novel x-ray imaging devices could provide significant performance improvements by virtue of substrates offering a thinner profile, lower density, and lower atomic number composition, as well as the ability to mechanically conform to non-planar geometries. One potential candidate for advantageous utilization of plastic substrates is that of a high resolution, indirect detection active matrix imager operated at mammographic x-ray energies. Such an imager, configured in an arc and operated in a back illumination geometry, could offer enhanced modulation transfer function and detective quantum efficiency by virtue of reduced optical spread in the scintillator relative to the optical sensor as well as reduction (or elimination) of oblique angles of incidence of primary x-rays. Motivated by such prospects, it is of interest to quantify the degree of performance improvement to be expected from such novel devices. In this paper, we describe a methodology under development by our collaboration to quantitatively examine the performance of indirect detection active matrix imagers incorporating plastic substrates. This methodology is based on the cascaded systems formalism with input provided by, among other things, Monte Carlo simulation of radiation and optical transport in the detector. Finally, illustrative examples of the use of this methodology are presented - although key input parameters are, as yet, insufficiently precise to allow the simulations to accurately depict the complete physical situation.