as said previously in past posts, it all boils down on how invitations/requests for alliance joining are handled. OW has a rather slowly and thoughtful process, while the other two are more gung-ho about new entrants joining, and this is reflected poignantly on the total financial situation of the alliances (ST and * are deep-down red, OW is the almost exact opposite). Perhaps given the current business climate, OW and its thoughtful process will be more enticing to potential suitors, but in any case the alliance has to overhaul drastically it approach in many areas, and the JL saga hopefully is the trigger needed.
For what I know and understood MH was quite advanced in its negotiations with OW (CX was the main sponsor) but at the end they tried again (unsuccessfully it seems) to join ST on the back of their long standing relationship with KLM. Also every some time there is a news story surfacing about combining MH with QF. All in all I think MH will join OW in relatively short time, giving both the relative uninterest of ST and the confirmed accession of GA, and it should not be too difficult wooing them, kinda low hanging ripe fruit for OW to pick.