This is a standard Usenet comment from Stallman, so I don't take it that seriously.

Tcl achieved many things, including the Tkinter GUI with a native look in Windows. Other projects like Python rely on it in the shrinking set of included batteries.

I would prefer if Lisp had won, especially in scientific code, but the C-API is not good enough. Unfortunately, currently Python is popular, so one thing is clear: People want a low level C-API in C with a published low-level interface. All other attempts have mostly failed in terms of popularity, so languages that want to take on Python better take note.