I think Emacs' process model is generic enough that it could adopt a better method of concurrency in the future. Functions for processes are run based on 'sentinels' which fire on interrupts from foreign processes. It's a simple model which works fine, and I would greatly prefer it to be augmented with a more clever scheduler than to dragging mutexes and condition variables into the system.

> At the end of the day .. none of this matters much, as we can evidently see since nobody has really tried to fix this.

Something that's easy to take for granted is how fast Emacs actually is. Anyone who's taken the time to try out an emulated Lisp machine will quickly observe how slow and clunky it actually is most of the time. And it's worth mentioning that a lot of the crucial components of the Lisp machine system, such as the windowing system, the garbage collector and the network stack work because they are written in a more structured and low-level manner so that they run efficiently and avoid consing. It is all Lisp, sure; but there's a bit of a bias that seems to portray that its all 'plain lisp' that 'just works' concurrently because it's magic.