I suspect that emailers are not dead but the risk to using them just got ratcheted up severely. Having Citi cut you off, even for a couple/few years is pretty mild compared to AA closing you down, especially for people with million+ mile accounts.
JonNYC seems to think this is the beginning of a wave and while he seemed quite unaware of the current mailer train, he has a long history of knowing what is going on inside AA. I certainly pay attention when he talks. If not for his warnings in 2010/2011, I would not have gotten LTG before they changed the rules.
I suspect the next couple of weeks will be illuminating as we will either see this expand or peter out.