Do you mean dbus as the other protocol? Because that's an intentional choice to separate out the protocol for drawing windows and responding to events and "desktop stuff" that's not related to being a window on the screen. They're not plastering over anything, that stuff is intentionally out of scope for Wayland.
The advantage is that anything can use the desktop stuff (cli tools) just by talking to dbus instead of having to be a wayland client despite having no windows.
Tons of stuff aren't in wayland that are actually graphics and window related. Wayland just forgot about it, then later on people realized that their design was far too primitive and simplistic.
DMA buffers, color management and pixel formats, scaling and DPI, image and video capture, tons of keyboard and mouse related things, all initially forgotten, now incompatible extras that are inconsistently implemented, frequently broken and forever in beta/staging/unsupported hell...
If you mean what Wayland literally calls "staging" it means that compositors should adopt it now, it doesn't mean pre-release. Once multiple compositors implement the protocol it can become stable.
The advantage is that anything can use the desktop stuff (cli tools) just by talking to dbus instead of having to be a wayland client despite having no windows.