cityfan,
--with respect to several points in your hypothesis. The claim that the purser threatened to tamper with the captain's meal was posted in another forum around the end of July, and labeled there as third-hand hearsay. (Unless the captain heard the threat directly, it would be second-hand hearsay at best.) So that point, presumably favorable to the captain, has been 'public' for a while.
From your post, the captain has yet to return to flight status, and the incident is now about five weeks old. Perhaps United's investigations of such matters move at a glacial pace. His certificate has not been suspended by the FAA.
Curiously, you raised the possibility that this incident was manufactured by two or more conspiring cabin crew who were aware that the captain was a recent victim of harassment by United. For them to test/provoke the captain in such a way suggests that there was a previous incident of questionable judgment or temperament on his part, else why would they embark on such a course of action?