SPG and Delta launched Crossover Rewards back in February (you can read more here). I broke the story few days earlier and had the original intended terms and conditions that did include space available upgrades on Delta flights for SPG Platinum elites (read more here).
This program feature was withdrawn before the official launch, however.
Now, Delta has updated the terms and conditions of the Crossover Rewards program and the day of departure upgrades for SPG Platinum members are part of the program. You can access the Delta’s web page for this program here, frequently asked questions here, and the terms and conditions here.
Here’s the terms and conditions part that deals with the SPG Platinum upgrades on Delta flights:
PG Platinum members are eligible for day of departure upgrades on most published economy fares on Delta and certain Delta-designated codeshare flights in North America within or between the United States (excluding Hawaii) and Bermuda, Canada, Central and South America, The Caribbean, and Mexico. Unlimited Complimentary Upgrades are subject to availability, may not be available on all flights or in all markets, and are not valid for travel to/from Hawaii, Transatlantic and Transpacific destinations. Complimentary Upgrades are not available on flights to/from South American cities that are serviced with our BusinessElite® product (i.e., Buenos Aires, Argentina; Rio de Janeiro and Sao Paulo, Brazil; Santiago, Chile; Lima, Peru; Caracas, Venezuela).
Essentially, flights within the Americas that are operated on the domestic style first class seats are available for upgrades. Flights that are operated on a proper BusinessElite seats are not.
Here are some frequently asked question by Delta that clarifies this upgrade program:
At the time of booking, your upgrade request will be automatically added to your itinerary and will be included on the airport standby list upon check-in for your flight. Standby upgrades will clear based on availability at the gate
For eligible flights, you will be given priority behind Medallions, Medallion Companion, and KLM, Air France, and Alaska elite upgrades.
You will continue to clear on the upgrade list based on your Medallion Tier.
SPG Platinum elite members who are enrolled in Crossover Rewards, do not receive additional benefit on Economy Comfort or Preferred Seats.
This upgrade benefit is highly theoretical, as the SPG Platinum member would clear only after all Delta and Medallion companions, KLM and Air France elite members eligible for upgrade, and Alaska elite members have cleared.
I doubt that there are many flights outside of some leisure destinations that SPG Platinum members would clear based on this program benefit.
Likely Delta and SPG felt that they had to do this, as the tie up with Marriott and United called RewardsPlus gave Marriott Platinum members full United Silver elite status (read more about United & Marriott partnership here). If they had matched the Marriott and United offer, Delta should have offered full Delta Silver Medallion status for SPG Platinum members.
Your upgrades on Delta are extremely unlikely to clear, as you are absolutely the last one on the list after all Delta, KLM, Air France and Alaska elites.