Regarding this subject I think:

  1. There's impossible to authoritatively classify anything as "dead code" unless there's a reference standard of what's core and what's not core (like, Java defines the JFCs). At this point it would be useful to have a reference standard of "core classes" and their "core messages/methods".

  2. Having a reference model, it would be nice to have a way preventing modifications of core classes inside official distribution. Meaning: to be considered part of an official pharo distribution, code must not alter foundation classes. That shouldn't be an issue due to huge support for inheritance provided by smalltalk. So, if need arises to have, let's say, a new message/method inside something like Array or OrderedCollection or whathever, it's easy to do that simply creating MyNewLittleOrderedCollection... It's not hard to verify integrity of core classes using digital signatures.

  3. There should be an official policy for marking code as "obsolete" or "deprecated".
I guess that once a model of reference classes is established, it's easier to start profiling things and finding what's alive and what's dead (not used anymore inside an official distribution). It also prevents the uncontrolled growth of "core stuff" as consequence of ad-hoc solutions.

A plus advantage of defining a set of core classes is that it makes easy to fully document and analyze  them. It allows to ensure several things that are required for any system to be used in the development of serious commercial software:
  1. Profiling (theoretical/measured): known algorithms
  2. Security
    1. Regarding continuous operation and up time
    2. Regarding "civilized" use of resources (memory, IO)
    3. Regarding integrity of data
    4. Regarding misuse & unforeseen uses of classes/messages/resources
    5. Regarding privacy
    6. etc...
  3. It makes it possible to have serious end user documentation, clearly specifying functionality, interfaces, cases of use, limits, error conditions, etc. (side comment: it never went into my mind de discourse of "documentation is the code" (moreover when some code is not easily understandable)).
My 2¢

CdAB