(maybecall (not (listp thing)) #'list thing) == (ensure-list thing)
i don't see in which aspect it is better than writing
(unless (listp thing) (list thing))
note that the rationale for ensure-list is that it's actually a bit shorter and also encodes the intention in a way that is much easier for a human to process (which, imho, can not be said for maybecall).
just my 0.02