There are further things to be improved:

* In `disk-usage--list-recursively', you make a loop over

             for attributes = (file-attributes name)

  This is slow, at least on remote systems, because you apply
  `file-attributes' on every file on a possibly large list. Maybe you
  could call `directory-files-and-attributes' per directory, instead.
  
* As said before, the commands you apply might vary on different
  hosts. For example, on my QNAP NAS server, getting du info on "/tmp"
  with "find /tmp -type f -exec du -sb \{\} \+" does not work. It must
  be "find /tmp -type f | xargs du -sb" instead. So the commands must be
  configurable per host. See for example, how `grep-host-defaults-alist'
  is computed via `grep-compute-defaults' in grep.el.
  
Best regards, Michael.