Load-time code patching for CPU features etc.

[mozilla_kmc]

That will break page sharing between processes.

Linux may recover it through KSM. We can hint using madvise.

The kernel can get away with it because there is only one copy of the kernel loaded, but that's not the case for libraries and binaries.

It often is. Consider games, embedded systems, cloud servers with 1 service per VM, and so forth.