@whitequark For x86_64, most structs between windows and elf ABIs are similar alignment if not the same. Also if done correctly the ABI for library would not expose any structs which will allow things even more.
As far as EH is concern, I suspect the library where this would be used the best for are ones which don't do any external calls just do stuff like encryption or some other kind of encoding/decoding like audio or picture or movies.