> Is there any compatibility with current X11 apps or every app needs to have wayland support?
Technically Wayland is totally different from X11. No compatibility. To get the compatibility you have to run them both: either start X-server inside Wayland or start Wayland server inside X.Org, both ways work, kind of.
In the long run Wayland is supposed to completely replace X.Org, meaning, every app would need wayland support, either explicit, or in toolkit it's based on.