The other thing to consider is if they end up putting JL into SkyTeam, DL is going to need to spend some time figuring out what to do with the NRT hub (and then doing it). I think that might be a priority over buying another airline, especially given that the AS/DL codeshares aren't fully integrated yet (a bunch of old AS/NW codeshares are now unbookable on the AS website), and they might want to get THAT running, too.