Something to keep in mind is that these 12? additional seats do not come with any additional overhead space, lavatories, or seating in the gate area's. All of these places will become more crowded.
It is also 12 more people that Flight Attendants need to take care of, and 12 more people that need to load and unload which will make boarding even slower.
I think this might be the last straw for me, since a majority of my routes have competition from SWA, Delta, and UA I will start price shopping instead of just being loyal to AA
Unfortunately, UA and DL will probably follow suit. SWA has also started moving in this direction.