> In either case, 'display-buffer' would look whether an appropriate
 > window exists and use that window, maybe also ignoring certain aspects
 > (dedicatedness, minimum size) that would otherwise prevent its use.

Attached find how a 'category' list entry could be handled by
'display-buffer-use-some-window' where a 'some-window' entry would be
given precedence.  Tested with

(display-buffer
  (get-buffer-create "*foo*")
  '((display-buffer-use-some-window) (inhibit-same-window . t) (category . foo)))

(display-buffer
  (get-buffer-create "*bar*")
  '((display-buffer-use-some-window) (inhibit-same-window . t) (category . foo)))

martin