For those still wondering if we have until Dec 31,2018 to qualify for Lifetime Platinum on the old criteria to get grandfathered into Lifetime Premier Platinum, this is the response from Marriott:
Dear xxx,
Thank you for contacting Marriott Rewards Guest Services.
With the information we have to date, with the Gold Lifetime Elite member status with Marriott Rewards you will be eligible for the Lifetime Platinum Elite status in the new loyalty program beginning August 1, 2018.
In order to be grandfathered into the Lifetime Platinum Premier status you will need to earn the Platinum Lifetime Elite status with Marriott Rewards. You will have until December 31, 2018 to earn this status with Marriott Rewards. You currently have xxx Lifetime Elite nights and xxx Lifetime points with Marriott Rewards. The nights and points that you have already earned with SPG will not be eligible towards the requirements. This will be the only opportunity you will have to receive the Lifetime Platinum Premier status.
You can find answers to other questions you have about the new Loyalty program at members.marriott.com.
If we can be of further assistance, please reply to this email.
Thank you for choosing Marriott.
Best regards,
XYZ
Internet Correspondence Specialist
Marriott Rewards Guest Services