We'll have to wait till later this year to find out. Plenty of people will be putting less on the co-branded AmEx (or no spend at all) while others are increasing their spend, perhaps to meet the $75K requirement for unlimited SC access or to continue to accumulate MQDs via CC spend. It's also possible it could take a a few years to see how this all shakes out for DL thanks to the rollover and such. Some people will be putting less spend since they don't need to chase MQDs due to rollover but may start putting spend on the card to bolster their MQDs once their rollover runs out.

Personally, this year will be an anomaly for me. With the rollover I have, DM for 2025 is within easy reach between my expected flying and CC spend. So most of my CC spend so far this year has gone on the DL AmEx. Next year, it would be a stretch for me to hit 15K MQDs for PM based on my personal and work travel patterns. It would be doable but not worth the pursuit in IMO since I will have GM by nature of my MM status and PM offers little benefit over GM based on my travel patterns. I'll instead retain/build status with AA and give myself more flexibility and the DL Reserve AmEx will become a sock-drawer card for the foreseeable future.