The MCP can already perform simple occlusion and reflection effects; however, it performs the effect on individual voices (in fact, the SB Live does that, too). In reality, a brick wall doesn't occlude all sound equally. The amount of sound transmitted depends on the frequency of the waves...
If the system works like I expect it would, the only real cost should be a reduction in the number of available voices.
Full physical modeling of sounds would not be something that could be done in real-time (modeling spherical pressure waves constructive/destructive interference, etc. is...