Wayland doesn't use something called "window manager". With X11, apps only draw contents of windows, and frame + title bar is drawn by window manager. With Wayland, like e.g. MS Windows, apps draw not only contents, but also the title bar, etc. This is why screenshots of gtk+/qt on Wayland show windows without title bar (it's simply not drawn at all by these toolkits on X11).
But about *compositing* managers... I'm not that much into Wayland
can somebody explain the situation with the window managers compositors etc on Wayland??
things like Kwin Metacity/Mutter Enlightenment Compiz just have to slightly modify the code to target wayland right??
see my above post. I don't know exactly, but I guess that the same is true for other X window managers as well. They all implement something that is very specific to X and it wouldn't make any sense to "port" them (read http://en.wikipedia.org/wiki/X_window_manager for example).
What are the benifits of apps drawing their own borders compared to sync fences?
The apps can have application-specific borders, like Chromium has. You could also do a lot of other creative stuff like merging and dividing windows, or making shaped, round/octogonal/etc windows, not only rectangular. Imagine a music player which has a playlist part, an equalizer part and a main control part. They are oval, but if you put them close together, they merge (using a pretty animation) to become one in whatever order and at whatever side you like.
The current X window manager paradigm doesn't offer the flexibility to do a lot of stuff. Look, for example, at Audacious. it can do some of the above, through native X features and assorted hacks, but it has some limitations. If you attach component windows together, you can still drag the whole composition around only by dragging the main window. You cannot merge them together so that it is essentially one window; it is visually obvious that it is several different windows stuck together. Also, dragging it around can produce visual glitches; for example, if you drag the Audacious window near a panel, it will try to stick to it, but the sticking effect only works with the main window, the rest seems to be dragged individually, unsticking them from the main window.