FYI, from Amex (Canada):
New Transfer rate: After August 4th, the transfer rate from Membership Rewards to Starwood Preferred Guest will be 1000 MR points = 1200 points in the new SPG program. Membership Rewards points transfers to SPG will be unavailable from July 27 to August 9, 2018. Learn more.
Under the current system transfers are 1000 Amex :500 SPG, then 3:1 into Marriott (resulting in 1000 Amex points to 1500 Marriott). Sooo... the transfer rate is going down.
Airlines are usually a better redemption option anyways, but for those hoping to make use of this, better get moving.