I have been a Diamond since the beginning and I have grown increasingly ambivalent about the program. As Delta once proclaimed "When everyone is elite no one is".
If this change happens it will either propel me to leave or step up my spending and stay. I had a lot of Amex Membership Rewards points with the 50% back on Amex Platinum Card. I used them for two flights in 2018...a China Eastern flight JFK-SIN in J and an Air France JFK-BCN flight in F. As I understand it I will get MQDs based on miles flown so I should easily requalify for 2019. I want to try one year with a "thinner herd" before I make a long term decision. I hope this change happens.