"El Gran Magnifico"
Mr Flibble is Very Cross.
The whiplash will be is if the system enables people to actually shorten their stay, and discourage longer stays.
Imagine the scenario where the parks get to the point where "Dad" decides.... no way I'm doing the parks without line skip.
Then "Dad" says.. "This thing cost me $1000 a day... I'll do it for 2-3 days, but no more then that.. that's crazy"
Then "Dad" realizes... if this lets us do all the rides quickly, won't I get through everything we want to ride in the park in 1 day? Why do I need to be there for a week?
Now Dad tells the family... "We're gonna do WDW, but only for 3 days... the line skip will get us to all the attractions we want". And all the other forms of entertainment that used to be diversions from the big rides will suffer because they can't all have immediate access to line skip. So the people hooked on line-skip will be more inclined to skip those attractions entirely or only do them if they need a filler.
So now Dad blows his wallet out by buying 2 days full of line-skips, but leaves after 3 days, instead of maybe staying longer. And Disney loses out on the longer stay... or maybe Disney sees it as "I ringed him dry even quicker, and now I got faster turnover"
If Disney enables a system where people can basically do a full day of DPA - those people are never going to want to be in the park without it. That's a double edged sword for Disney and their pricing strategy.
Yes and No. I don't necessarily disagree with your main point of possibly having a negative effect on duration of stay. But that's assuming that - that family is only interested in going to parks and riding rides.
We don't yet know how this is all going to work and I'm going to speculate that DPA is not going to have a park-hopper component (If it does it will make it even more expensive). So to get the whole Disney experience from DPA you'd be looking at 4 days. Then you have resort time, alternatives like Springs and/or Water Parks, Boardwalk etc.
There's another factor you're missing that supports your example. If someone is laying out the money for DPA, their main focus will be rides. They'll want to get on as many of them as they possibly can within the window they are at the parks. They won't be concerning themselves with spending an hour and a half doing a TS meal, a character meal, or wandering around gift shops. I would think that the average spend for that family in the parks for F&B and merch would be less while utilizing DPA than it would be without. And I think some (probably a lot) will sacrifice some of their meal and merch budget to offset some of the DPA cost. And yes, it could also turn what used to be a 7 day vacation into a 5 day one.