The CrankyFlyer article that JDiver linked to is great.
It is a great read, and the actual agreement linked therein, while dense is worthwile as well. As my prior post lays out, I disagree with Cranky that boosting the experience for elites is the key. If the partnership provides a broad portfolio of destinations for non-elites, AA credit card holders and even retired AA loyalists to earn/burn miles, as well as better combined schedules out of LGA/BOS on "secondary" routes (by AA standards) for AA corporate accounts (who will have to fly AA code to get their corporate pricing), it may be sufficiently successful for AA.
The idea that there will be anything close to metal neutrality from a customer perspective seems more remote than before. In fact there is a temporary/experimental tone to the whole endeavor, which to be fair may have more to do with being in uncharted territory than an expectation it will all come to an end when AA wants to re-assert itself in NYC.