Volcano Bay is a 100% virtual queue park. You can’t do stand-by for the slides, you have to get a return time. It was part of an effort at Universal to switch to virtual queues that also included Jimmy Fallon’s Race Through New York (which opened without a stand-by queue) and Fast & Furious Supercharged (which was also not supposed to have a stand-by queue). When Volcano Bay opened it was a crowded mess. The things people expect to just be available at water parks like the lazy river were full. The waits for food were horrendous. Universal botched the park capacity calculation and had to reduce how many people they admit to the park.
Virtual queues require more space and more capacity than stand-by because people are still there. You need a place to put them, to give them something to do while they are waiting outside the physical queue. Theme parks are an even bigger puzzle than a water park because lounging around, swimming in the wave pool or drifting along in the lazy river are expected parts of a day at a water park. As much as people like the PeopleMover, just sitting on it for multiple rides right through is not something a large portion of visitors consider a key part of a visit to the Magic Kingdom.
Volcano Bay was supposed to be the big kickoff to Universal’s bold new queue-less future and instead it was the end. Universal Studios Beijing is not a virtual queue park. Epic Universe will not be a virtual queue park.
And when even the People Mover has a 45 minute wait with a castmember standing beyond the stage in the direction of Space Mountain with a "line starts here" sign, you know you're in trouble.
... Unless you're Disney which means you've right-sized things, I guess.
In the case of Race Through New York, the virtual que works well since that's not a popular draw which sounds like a knock but really, it allows the attraction to fit the space really well in a way that something that would require a standby line wouldn't...
But the other problem in terms of the parks IMHO, especially MK (I'm thinking a big part of New Fantasyland), is that when you start having to create more space for people to stand around in because you're pushing VQ systems you're also eating into potential attraction space be it smaller experiences or streetmosphere space* or what have you.
It also makes smaller attractions kind of impossible because they'll be swamped with people. In general, it makes the smaller more intimate experiences that allow guests to get closer and be more involved really hard to pull off without using an upcharge or some other method to force guest to opt themselves out of it.**
Going back to Universal after a long hiatus while I waited for my son to grow into the experiences there, the thing that struck me most was... the number of places to sit down available in those two parks. People weren't sitting around on the ground off in corners like tiny little homeless encampments. There were still benches and seats and things of that nature all over the place and they weren't just full of people monopolizing them - you didn't have to fight anyone for a place to sit because there was no scarcity of available space.
It's
so weird what WDW has become.
*Of course, they'd rather not pay for this anymore so no big loss for them, right?
**Also not a problem for Disney, I guess, but it sure creates the "what did my ticket even buy me?" feeling when people get in and find out that whole experiences are designed around required purchases set at prices higher than admission. 
