What were the proposed changes to the Delta loyalty program in mid 2023, and why was there such a backlash, and how is it set up now?
After a lot more reading, the article @jcaron pointed to was a great start....
There are lots of changes for the "elite" levels, but I (and I assume most people) are "just" trying to get silver/gold medallion status. For these levels the changes are substantial.
In 2014 Delta moved from a pure "miles" based program to a "miles" and "dollars" based program. You needed a certain number of miles, and a certain number of dollars spent to achieve various levels of status.
The big change for 2024, is to drop all mileage requirements and to significantly increase the dollar requirements. This chart from this article pointed to by jcaron thepointsguy.com/news/delta-skymiles-changes-update really summarizes the changes well:
On top of this, the dollar amounts are just money spent on airfare. You can get a SkyMiles card, but you only earn 1$ for every $10 spent (or $1 for $20 depending on the card) and no benefits for spending it on hotels etc.
This is a relatively significant change for this program, and a significant change in the industry. Thus the blowback.