I agree that codeshares used to be much more important than interline agreements, but considering the two airlines AA/JB dont use the GDS companies like Orbitz/Expredia/etc then the codeshare benefit is reduced. Since all the traffic now has to book on aa.com (or get info directly from AA) then they are able to "push" the interline itineraries. Jetblue makes a big deal out of every interline agreement they sign, and I think they are onboard with this idea of not using the GDS and controlling their inventory.

The jetblue interline agreement has benefits for frequent fliers, which typically arent included in interlines, and if it is developed further to the point where elite frequent flier mileage can be accrued then that all but eliminates the need for a codeshare.

Domestic codeshares have to be approved by APA, but not interline agreements. AMR wants to have companies like jetblue do their feed flying in the future through these types of agreements. Jetblue feeding AA doesnt require a CPA or any sort of financial support from AMR, they simply run their passengers through major AA hubs and AA picks up connecting pax to int'l flights. If I were APA, I would be 10 times more worried about this than Eagle flying an RJ to Des Moines.