I would be rather surprised if AS formally joined any alliance as well. They have very effectively played "Switzerland" - gaining partner revenue and mileage redemption opportunities that exceed the major alliances. I rather doubt joining one of the majors would outweigh the resulting losses.

About the only thing you might expect AS to do is grab some continued 'goodies' as convenient. (e.g. the limited upgrade reciprocity with NW or the full club reciprocity they have with CO and NW).