I bought an AMEX Pay With Points ticket for DL first on 04/13/2017.
I have AMEX Biz Plat and AMEX Personal Plat.
I used AMEX Personal Plat for the charge.
Received "Congratulations! Your flight redemption qualifies for the 50% Airline Bonus" email on 04/14/2017.
Have not received 50% rebate yet.
My partner bought an AMEX Pay With Points ticket for DL first on 04/13/2017.
He has AMEX Biz Plat and used AMEX Biz Plat for the charge.
He received "Congratulations! Your flight redemption qualifies for the 50% Airline Bonus" email on 04/14/2017.
He has not received 50% rebate yet.
So, am not worried yet about not getting 50% rebate due to putting the charge on AMEX Personal Plat.
However, given this new 04/11/2017 guidance and the current delay, my advice to others would be to forgo the 4x bonus from using AMEX Personal Plat.