People with multiple displays are definitely going to be a minority. And not all of them will be using virtual desktops. And not all of those might have an issue with how they work now.
Yeah ... I'm one of those people who like the way they work now. I really hope that the current behavior will still be achievable in the new system.
When I switch virtual desktops, I want every screen to change. Each virtual desktop is a different project, and most of those projects are spread out over multiple screens. When I switch between projects, I want all of it to switch to that project. And if I want something to stay put while switching, well, that's what 'move to desktop --> all desktops' is for. (Honestly, I think most of the people clamoring for this new feature simply don't know how to use the 'show on all desktops' feature that already exists.)
I've got 6 screens and 8 virtual desktops. If I have to switch each screen's desktop individually, that's going to be a huge pain in the ass. I really really do hope they include a way to lock all screens together and make them all switch at the same time every time, just like the old behavior.