This is more or less what we once dreamed of doing with Activities in KDE 4, but couldn't make it work on X11 - we were banking on the X11 session handling protocols to implement the suspend/restore, only to find that few if any toolkits and apps implemented them properly, and that fixing this wasn't going to be viable due to a lot of spaghetti all over the place.

This is partly why Activities ended up feeling somewhat redundant to Virtual Desktops. But if you go back to those early 4.x releases, you will find that the Pause/Unpause buttons etc. on Activities were featured rather more prominently.

As David describes in the blog post, things in Wayland are a lot more nicely layered. In part, toolkits have also seen architecture cleanup as a side effect of having to support multiple backends during the transition, and code has become more hackable and modular as a result.