I’m not sure we want to copy the Windows startfile call for other OSes.  The os module is designed to wrap system-level calls, masking OS differences (for sendfile, for example) but not going further; it’s up to other modules (like shutil) to build more convenient APIs on top of what os provides.  xdg-open is a program that’s used to open files or URIs, but it does not provide other actions like Windows’ startfile does (edit, print, etc.), not is it backed by a system call.  For these reasons, I think it’s inappropriate to implement os.startfile for non-Windows systems.  People can use subprocess to run open or xdg-open.