Well, considering that Emacs is supposed to integrate smoothly with external processes, it looks that asynchronous IO support it will be a better solution. Multithreading is generally a tricky business for interpreters and virtual machines.

So to reduce editor interface freezing, looks like a dead-end: either you expose asynchronous IO (like AJAX), or you add the complexity to have a multithreaded interpreter (like JVM) or implement a sane concurrency model (like the actor model in the BEAM machine). Or else avoid Emacs modes that are known to freeze.

However, I recently discovered that VIM uses threads:

  $ ps -eLf | grep vim
  UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
  etanol   15073 15023 15073  0    2 22:23 pts/2    00:00:00 vim
  etanol   15073 15023 15074  0    2 22:23 pts/2    00:00:00 vim

I wonder what for :-S