[fayalalebrun]

Yes, desktop applications need to implement the Wayland protocol in the same way they need to implement the X protocol. There is a compatibility layer called XWayland which allows you to run Xorg programs under Wayland.

However, running programs under XWayland comes with issues such as lack of proper fractional scaling. This means that although not strictly necessary, from a user's point of view it is desirable to have applications move to Wayland.