Many scripts on one system are inconsistent. Things will be more user-friendly by only using one language for most tasks. No more Makefiles, rc.d/, loader.conf, .xsession, .profile or AUTOEXEC.BAT.
The system which know how to start/stop services. And the system which boots your machine(s).
As many applications as possible should be written in Ruby. For instance there are no need to implement a nice GUI calculator in 5000 lines of C code, which compiled occupies 500 Kbytes. Such applications should be written in Ruby, so that its easier for the user to adjust the application for his paticular needs.
If the processing demands are too high, then it may be necessary to do certain things in C/C++/Assembler. Then SWIG can easily wrap the library, so that it can be used within Ruby.