Based on current environment, I suspect Citi will not allow churning forever. I just don't know when it will close this loophole.
Contract to others, I actually current have 0 Citi AA card and just plan to get first one. I was too busy for other bonus points for Citi TYN card previously.
Luckily I at least get 2 cent per point this Feb. Now TYN is nearly dead so I will try get several Citi AA cards.