FWIW I think you could say FFI is possible. I've written a Golang module for emacs and build using -buildmode=c-shared and loaded it into emacs. I think for generic FFI you could probably wrap some sort of libffi.so using elisp.
The problem is not technical, but political. For years, RMS has opposed an Emacs FFI due to his belief that it could be used to subvert Emacs goals by making it possible to do proprietary extensions.