Here the official answer received by SPG platinum liaison :
Thank you for reaching out to us regarding One Program, beginning this August. I trust your day is going well and it is a pleasure to hear from you.
Members who achieve 100+ eligible nights plus $20,000 in eligible spending between both programs in 2018 will receive the Platinum Premier Elite status with Ambassador service. Members who stay 100+ eligible nights with SPG in 2018, will also have the Platinum Premier Elite status with Ambassador service honoured.