One of the arguments towards the "we don't need to upgrade the Common Lisp specification" attitude is that if we have multiple different implementations, each with its own interface to implementation-defined functionality, then we can successfully unify that interface as the language's users, without changing the underlying language.
Portability libraries that offer uniform syntax for features that implementations define differently are the de facto standards in the Lisp community. To name some examples, networking (USOCKET), multithreading (BORDEAUX-THREADS), accessing the metaobject protocol (CLOSER-MOP), GC and weak data structures (TRIVIAL-GARBAGE), accessing the filesystem and operating system functionalities (UIOP). There are many others.
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At the same time, I agree that the specification needs an upgrade. As soon as I find some time, I'll try to think of means of organizing such a committee and, if required, securing the funding for it.