Personally, I suspect that if the Wayland developers simply dropped maintenance of Xorg completely--no more patches, no more XWayland or at least completely disassociate XWayland from Xorg--that a community would step up and carry Xorg forward. As it is, that erstwhile community remains largely hidden, maintaining out-of-tree patches. But if that community faced the prospect of 1) being able to take back the reigns of Xorg, and 2) if not, Xorg vanishes today, then it would likely become much more motivated, organized, and proactive. (Whether it would be capable of carrying Xorg forward is a different question.) Alternatively, it might create the environment for projects like Arcan to shine.
I don't. That community was sorely needed several years ago, but failed to show up.
Only the compositor has access to the composited image therefore is the only program able to make screenshots and full screen sharing. Furthermore, efficient sharing of single application windows is only possible with direct memory access to the buffer which also is something the compositor does/has. The Display protocol is the only sensible place to negotiate access to GPU resources.
No, GPU resources can come from any number of other places. That's literally the purpose of direct rendering. Any applications using GPU compute can produce them without requiring a connection to the display server. There's no reason to put that in Wayland or restrict it to the compositor. There's already a much better protocol for sharing GPU buffers: Pipewire. Dbus is only there to act as the glue between a Wayland compositor and Pipewire.