The assumed benefit is creation of an abstract API.

The problem is, whether you action inputs in the current thread, or in another thread has nothing to do with abstraction: it is an implementation detail.

And abstraction might be something like a subroutine called: enact(). It might be used something like:

while( my $decree = <STDIN> ) {
    chomp $decree;
    enact( $decree );
}
[download]

You can now implement enact() is any number of ways: as immediate code as an if/elsif/else cascade, or a dispatch table; or passing the responsibility off to a concurrent thread or process via a queue, pipe, socket or shared memory. Whatever.

But as currently coded, there is no abstraction. (Other than the use of a queue and another thread, and they add complexity rather than hide it!) And you are gaining no benefit from the use of concurrency. It will take at least 2 context switches to go from reading an input to the point of having enacted it. And a context switch will take 2 or 3 orders of magnitude longer (x100 or x1000) than processing the input inline.

All you've achieved by multithreading that data path, is to use more memory and make things slower. Now given that all of the inputs you've outlined can be processed far more quickly than a human being can type the next command, there is no benefit there either. You would only benefit if the inputs were being supplied by another program or computer faster than you could process them inline. And even then, unless the input stream was bursty, all you would do is fill up the queue with commands faster than you could take them off and process them.

Voltaire (apparently) said: a book is not finished when you can add no more, but rather when you can remove no more. And nothing is a more laudable and beneficial goal in code development, than removing anything that serves no purpose.