As far as I understand from the XDC presentation video, it wouldn't be implemented in the toolkit, but as a special wayland compositor. On the computer you want to display the window, you would run the regular weston compositor, plus some client software. On the machine the application runs on, you would instead run some special compositor that speaks the wayland protocol, but sends the buffer over the wire instead of displaying it on the local display. Therefore, you wouldn't need anything special in the toolkit. Note that I don't know any more than what I learned from the talk, so take this with a grain of salt.