The reason you care is because if you remove the GIL, you can write a 1:1 or green-threaded M:N library (actor model like Erlang, or dataflow like Oz, or whatever other models floats your boat) once in Ruby, and then a rite all the application code you want using just Ruby.

Using scripts running in separate OS level processes -- no matter what infrastructure you use to connect them -- isn't necessarily the ideal solution.