Correction: AA is capping J seat sales on the 787-8 only, not on the 787-9.
The thread title has been modified to reflect that.
American is making one other major change to their 787-8s. While these planes are being reconfigured, they’re going from having 28 business class seats to having only 20 business class seats, which is obviously awful news in terms of upgrade and award ticket odds, and even in terms of finding cheap premium fares.
This “loophole” allegedly favoring upgrade possibilities will only apply to unconverted 788s, and that number of aircraft will diminish through ~June, when all 788s will lose eight Business seats and gain Premium Economy. That and unplanned equipment changes make this device temporary and less useful than it appears, but it will help AA not leave eight passengers with Business seats dumped with equipment changes - smart move, AA.