I'm Platinum Medallion, yet I am noticing that First Class upgrades on Delta (even after February 1, 2016) are harder to get. I believe that one has to be Diamond now to get First Class upgrades.

I wrote Delta to discuss this; I would like your feedback. This is what they said:

Delta continues to offer you access to unlimited Complimentary Upgrades on eligible flights if First Class seats remain unsold during the Medallion upgrade window or at departure. Over the past few years we have seen demand for premium services increase and many customers are now interested in customizing their travel experience. As a result, we have offered customers the ability to select a premium seat after they have made a Main Cabin purchase or during the check-in process since 2011, but also retain unsold First Class seats in eligible markets for Medallion members. With the advent of Smartphones and mobile functionality, paid post-purchase First Class service has become increasingly popular.

Offering paid First Class options gives you the option to confirm a premium seat in advance or to continue to standby for a Complimentary Upgrade. Subject to availability, Delta offers SkyMiles members the ability to purchase a First Class seat using miles or money, and Medallion members may continue to standby for complimentary access.

Given that demand for paid First Class seats is on the rise, a popular option for Platinum and Diamond members is to select upgrade certificates in the Choice Benefits program and request an upgrade using Global or Regional Upgrade Certificates.