Alaska's partnership with American is at about the same level as it's partnership with Delta, if not slightly worse. For example, Alaska has long offered access to DL Sky Clubs (although Delta scaled back access rules for everyone, including Amex Platinum Card members), but Alaska and American only recently improved their own lounge agreement. Alaska and Delta continue to have reciprocal upgrade rules, while there is no policy for reciprocal upgrades between Alaska and American.

I don't think anyone is talking about Alaska joining SkyTeam.