IF... and its a huge "if" the alliance would basically replace the relationship CO currently has with NW, this would be a HUGE win for AA elites. Heres how the CO / NW arrangement currently works, afaik:
1. Codeshares with full tier-by-tier equivalence of elite members on each others carriers. This means that CO elites are on even footing with NW elites and vice-versa for domestic upgrades - regardless of whose metal.
1a. Caveat: #1 could be very tricky to implement when one carrier has unlimited domestic upgrades (CO) and the other still plays the sticker game... DL and NW eventually replaced their "sticker" equivalent with policies which essentially match CO's. Also, CO elites would have a significant status-attaining advantage in that their top tier, Plat requires only 75k EQMs while we all know that EXP requires 100k EQMs or EQPs.
2. Full cross-compatibility of lounge memberships... for both domestic AND international routes (eg: a CO PC member currently can use the NW WC lounges in NRT, ICN, etc... regardless of whether the PC member is flying on NW metal or even any Skyteam metal). This would be a pretty huge gain for AC members, as CO lounges tend to have things most global elite travelers expect... like free internet (yes, i know that ACS are finally handing out t-mob cards) and more importantly, free booze. Who knows, maybe AA could finally buy a friggin clue and make drinks complementary in ACs (or at least beer & wine).
All in all, I think AA could become a much better carrier if it were to partner with CO and adopt some of CO's best practices. On the flipside, CO could piss off a LOT of its elites if it were to partner with AA and adopt some of AA's WORST practices.
IMHO, the AS model is the WORST possible scenario. AS strikes me as an airline wh*re who will partner with anybody they can (except UA) in order to "stick it to" UA.