Wayland has a bonkers security (theatre) model based around protecting from untrusted processes (graphical applications) connected to the compositor. (If you must give untrusted code a process on your machine, the correct solution is to give it its own Unix user and run an X Windows server owned by the same user.)
One consequence is that screenshots/screencasts do not exist on Wayland, applications can only see their own windows. Also, quoting Red Hat: "Furthermore, there isn’t a standard API for getting screen shots from Wayland. It’s dependent on what compositor (window manager/shell) the user is running, and if they implemented a proprietary API to do so."
EDIT: Other stuff that you can not do with Wayland and is justified by their "security" model is injection of input events and reading other applications input (think xdotool, autohotkey; this is great when you want more control of your graphical user interface system).