AFAIU, this thread has turned to be about interfacing whatever app
to a scripting language. I consider this a very usefull feature for all
but basic applications. In particular, I consider that interfacing init
- The init program which is pid 1 - with a scripting language would
provide ultimate "init freedom". There are few things the shell cannot
do well enough to be a good init program; but I don't think it is
possible to interface an application with the shell, I mean let the
shell execute commands belonging to the application without forking a
process.

     To come back to the list of scripting languages, I remember one 
very nice feature of Lua: AFAIR it has built in multitasking primitives. 
Another language was designed precisely to be interfaced to 
applications: Tcl. With Tk, it also involves the toolbox to make a GUI.

     My two cents.
                             Didier