Overall, what I'd expect this to do in the aggregate is to lock people more into the flights onto which they were already booked. I'm not sure that's a good outcome when capacity is restricted as much as it is.
And thus book the flight they think they'll need or actually need. Like I said in the above post, it's no secret, as evidenced here on FT, that people will book a later flight that's significantly cheaper, knowing there's a good chance they can SDC to the earlier, more expensive flight on the day of, and save a chunk of change.
I'm not saying I agree or disagree with the new rules (if they're true), but merely that if that's part of the logic, then I understand the move by DL. What I think you're seeing through these "enhancements" (such as MQD and the SDC changes) is DL amending the perks so that they're used in the way they were designed to be used and remove the ways that they're taken advantage of.