> The patch appears to change it to 2 in tkinter/__init__.py.

This is for development only. You can apply the patch and test how new mode 
affects IDLE or other applications.

> One thing slightly puzzles me: the current PythonCmd is used in a call to
> Tcl_CreateCommand.  (Since the latter is not in _tkinter, I presume it is
> 'imported' in one of the includes.)  The new PythonObjCmd is passed to
> Tcl_CreateObjCommand. Does that already exist, just waiting for us to add
> PythonObjCmd?

All Tcl_* functions are Tcl C API functions. Old functions work with strings 
(char *). Modern functions (have "Obj" in a name) work with specialized Tcl 
objects (Tcl_Obj *).

> I near as I can tell, the only differences between PythonCmd and
> PythonOjbCmd are /argv/objv/ and the following.
> 
>       PyObject *s = unicodeFromTclString(argv[i + 1]);
>       PyObject *s = FromObj(data->self, objv[i + 1]);
> 
> I think I would make the name substitution either in both or neither.  It
> would be nice to reuse the rest of the code.

I'm not sure that I understand all you mean, but in updated patch the common 
code are extracted to separate function.