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No, I do not know of any platforms where the current Sleep()
implementation in Tkinter would not work.  That aside, I
believe that there are still two issues with using Sleep().

From previous experience with Tcl/Tk (non-Python), I do know
that events tend to pile up in single-threaded, event driven
applications which use Tcl timer events.  In such
applications calls like Sleep() or Tcl_Sleep() should be
avoided entirely.  Using Tcl/Tk timer events is a far better
approach in this case, for reasons mentioned earlier.

I'm not familiar enough with Tkinter, multi-threading and
the impact of Sleep() in Python.  However, instead of using
Sleep(), what about yield() or some similar threading
function?  And compile that call only in the threaded Python
build?