Define "help". With the new caching rules, there is just no way two sites with different TLDs can share asset caches, so it wouldn't help in the sense that double downloads could be avoided.
True, but the "avoid multiple downloads" part is most likely more significant than the "avoid multiple copies on disk" part. Storage is comparatively plentiful while network bandwidth is often quite scarce, and 3 seconds longer loading time are going to be more visible than a 10 MiB larger disk usage.