How can order I discussions by (inserted - updated) date in (ascending - descending) order using API V2?
It is not currently possible, the getWhereRecent method of the discussion model doen't influence the order.
grep is your friend.
there is a BeforeGet event in the discussion model where order can be influenced, but this wouldn't be influenced by a call parameters.
I suppose you could make plugin that detects call parameters on discussionsApiController_indexFilters_handler then process that value in discussionModel_beforeGet_handler setting the OrderBy event argument.
this is all becuase getWhereRecent doen't actually consider order. it calls getWhere which does.