Not surprising. If AA and US merged (Or US took over AA, whichever way you want to describe it), both the merged US/AA and United staying in Star would really not be an option, from an antitrust standpoint.
No way that the antitrust authorities would allow two of the remaining large carriers to remain in one alliance.
So, no real news here. If they are thinking about US/AA I think they have to think OneWorld, since I think United has the right to stay in Star as the more senior member.