the base game will be the same each patch/installations. Therefore, the "list of binaries" can be populated as well. When the game starts up for the first time, it scans the non-included XMLs (for mods). It would then parse the mod data and add that to its list.
And... I'm pretty sure an installation can be just as powerful as a game? What magical property does a game have that enables it to be multithreaded while an installation can't be?
In fact, unpackers/packers tend to LEAD the multithreaded application and set the standards (along with encryption/decryption). Read about the effect of CAS RAM timings, you'll see that the speed and timings of your RAM are FAR FAR more important for basic packing/unpacking applications such as WinRAR than they are for a video game such as Crysis.