Chances are indeed slim, but it should still be there as a friend received one to Chicago in Feb.
In the summer season with full flights it surely is less likely, nobody really wants to go to Chicago in Feb if they donīt have to so flight was wide open in all classes.
I personally have never received one in 5 years, but I fly mostly either premium heavy routes/days or already book business class. Also keep in mind SAS pushes heavily upgrades, both paid and points, and those are most likely prioritized ahead of courtesy upgrades to Diamonds.

I never count on it.