When an application is drawing stuff, there's plenty of cases where you have to wait for round trips from the application to the XServer too. Plus the application, X and window manager can all manipulate the same properties of a window, so there are plenty of cases where you can't be certain what will actually happen.
I prefer to think of wayland returning to the unix philosophy of doing one thing and doing it well. It takes over the job of rendering multiple windows on a single desktop, and forwarding mouse and keyboard events to applications. Everything else is out of scope. Is Wayland doing that job well? Maybe, but I'm not an expert.
If you want to display an application that talks X11, or connect to another server via RDP or VNC, do that with another program. If you want to innovate in this space, go ahead. Build a GTK or Qt remoting protocol or something. Having a clean separation between network protocol and display compositing should help the ecosystem in the long run. I will say that the X11 wayland client isn't that good, I've seen plenty of weird bugs when using old applications.
The big challenge to adoption is the conversion of existing applications. Even if you are using a high level toolkit, there are bound to be a few X11 library calls hanging around.