I don't have a great answer for this. Why they feel they can implement this new arrival system for a race that's several months away, when the language for that same race appeared several months ago? That's to say, they've had plenty of time to implement whatever they're planning for Princess for Wine and Dine. At least on the surface it would seem they did. I can't imagine it would be overly complex, otherwise they probably shouldn't do it.
My best guess. They want to see how Wine and Dine goes without these new arrival time procedures. If things go well, then the language of arrival times for starting groups will disappear off the Princess website because it isn't needed. If Wine and Dine doesn't go well, then they've got this other system in their back pocket for Princess.
"manage the flow of participants from the staging area to the start of the race."
This to me reads a lot like what they currently do for the 5k/10k. Hold us in an area away from the start line. Then they approached Corral A and walked them up to the starting line. At the back of Corral A at the start line it was empty. And then at some point they walked up Corral B to the start line.
Whereas in the past, the HM was all corrals lined up consecutively. There wasn't a holding area separate from the starting line. Rather, as corral A was released, all other corrals were slowly walking up behind it towards the start line.
So a potentially slightly different way to go about the starting line procedure for the HM. I suspect this may play a role in further spreading out the runners when you have an assigned arrival time as is being currently proposed for Princess. So I suspect their full plan for "utilizing Start Groups to follow health and safety guidelines and manage the flow of participants from the staging area to the start of the race" isn't being fully realized for Wine and Dine.
I suspect we'll continue to see mini-waves. You can visually see the mini-waves in this graphic from the 2018 Marathon.
View attachment 618960
There were eight corrals for 20,000 runners. However, there were 25 total mini-waves in the race. So that's their way of slowing the flow so 3,000 runners aren't all released at the same time despite all being assigned s3, or in the previous case Corral D. Now instead, you'd break the people into four groups (s1 through s4) but can still have the 25 total mini-waves if desired.
View attachment 618962
That remains a possibility. Although the language on the Princess page of specific arrival times for starting groups leads me to believe the language of corrals is gone. Conversely, corrals still exists on the FAQ page for club runDisney. Thankfully we'll see soon in a few days when people begin to pick up their bibs.