The problem is you don't get to open up routes without authority, and right now, there's no additional authority to mainland China, and only limited opportunities to Japan.
You may be right, but I thought that there were still some unclaimed frequencies to China; AFAIK, AA claimed seven for LAX-PVG as did UA plus I think that DL claimed seven for its SEA service, but I thought there were more left over after the 2008-09 meltdown when nobody was fighting to get new frequencies.
I remember hearing that additional NRT frequencies would be made available this year - but no recent news.
Assuming that most US frequent flyers were giving their Asian business to UA, the merger should provide some turn-key passengers to China, Japan and beyond if they stay with the new merged AA. Don't know if they add up to enough passengers for more than one or two flights, but that would seem to be easier growth than building it and hoping to take away business from UA or DL. Of course, if UA doesn't right their ship, AA might be able to take away more from UA.