I think introducing a deeper discount economy fare limiting mileage accrual/upgrade eligibility would be reasonable (not that AA cares what I think is reasonable--but I wouldn't be too upset)....

What would really be upsetting is a major change in award travel redemptions and required amounts (I guess devaluing miles) in addition to the deeper discount fares. That's the biggest draw to AAdvantage for me. Everytime I have to book a work trip, I see it as an investment in my leisure travel ^