I think some people here might be misguided in that they think CSD means the toolkits have to draw the decorations.
The way it will most likely turn out to be is that everyone will use some sort of 'libdeco' to do the drawing instead,
actually unifying decorations even across compositors, something that wasn't even possible under X.
Absolutely NO Xfce, Plasma, Unity, etc. would want to use a GNOME application that cannot be minimized. Unity users wouldn't want to use applications with titlebar buttons on the righthand (i.e. the “wrong”) side.
Client-side decorations also mean that the application is the only one to decide what happens with a window. So when I load a huge file into an applications and while processing the file the UI becomes unresponsive, I won't even be able to minimize it.
IMO it's evident that Intel develops Wayland for tablets, smartphones and other devices (smart TVs, IVI,…) that don't have windows and that's fine but then Intel should not act if Wayland was for desktops as well.
No one is seriously denying that X accumulated tons of cruft over the decades but attempting to replace it by even throwing X’s good aspects out of the window is absolutely retarded.
In other words, if you use an efl application in Unity, it'll integrate poorly. Oh wait, it would anyway.
What it really means, is if you use [insert wayland incompatible toolkit here] in Unity, you'll get a rootless X window which is nested inside the wayland compositor, and will have the same decorations as all of your other windows (the compositor which contains the X window, which is part of the toolkit you're using (GTK, Qt, etc.), will use your current theme for that).
The only thing which may be off would be the color scheme and the actual application feel (because the wayland incompatible toolkit may not utilize the same theme library). That would be, and is, the case now anyway. Hopefully it will be improved in the future, since color schemes can be relatively simple to represent. It'd be up to the toolkits' developers to decide whether it's worth their time, though.
Hopefully, any toolkits which implement the wayland api will also implement this ethereal new theme specification. I've heard it theorized a few times, and I believe it's possible, but I haven't heard any news recently about it. Here's hoping. ^_^
It's entirely legal (and was proposed on the wayland list) for the compositor (Weston, KWin, etc.) to override the default appearance of the app in that case.
That allows the compositor to stick custom menus, or draw it's own titlebar + buttons on top of the hung app, and the compositor is free to force close, minimize, help drag the window, etc. to it's hearts content.
I don't have a link, but i'm sure you can google to find it if you want.