This sounds very much like... prelink?
You can definitely do most of the same process in hacky ways on Linux already. I don't think you can use it for making the merged shared lib to use for compilation later... But it's only a few hacks away.
> Mergeable metadata roughly doubles the size of the dylib.
I think they just bundle the static lib and dynamic lib together. I think there is a wasted opportunity to do something much smarter here, but maybe that will follow.
We already compile static libraries with PIC, and use the same object files to compile dynamic libraries. In theory the two could be bundled in a way that shares most of the data, as the machine code is literally the same. They are both linked from the same object files.
At some point the difference does seem to become mostly "what do you do during linking".