Odd - this is what I got when I emailed Marriott today. It looks like we have gotten different answers from the same people.
Thank you for contacting Marriott Rewards regarding Lifetime Elite status.
We have an Emeritus (Lifetime) status that offers Elite levels after certain criteria have been met.
Emeritus Platinum status is offered after the following qualifications are met:
Guest has been a member of Marriott Rewards program for 12 years, with at least one year at Platinum Elite.
Guest has stayed 1000 nights over the history of the Marriott Rewards account.
3,000,000 total points earned during the history of the account.
For Silver, the night requirement is 600 nights and the point requirement is 1,500,000.
For Gold, the night requirement is 800 nights and the point requirement is 2,000,000.
There is no way to request this status unless the qualifications have all been met.