hyperspec-lookup at a blank prompt in a *slime-repl* will set the read-only/intangible package prompt as the default for the completing-read in the minibuffer.
the read-only bit should probably be stripped. that way the user can easily delete the text in one keystroke if it's an intangible package prompt or edit it if it was grabbed from a read-only lisp source buffer.
i'm an elisp newbie, so i don't have a working patch yet. i imagine it involves either (remove-text-properties ...) or copying the text with no properties. someone want to point in the right direction?
thanks,
...bryan