TL;DR version: you are incorrect on nearly every claim you make.
> 2. X.Org is running as Wayland client. Meaning, Wayland talks to hardware, X.Org talks to Wayland, and all X11 apps run through such X11-to-Wayland proxy.
Yes. X11 apps run on an X11 server with Wayland being the backing graphics output and key/mouse input.
> It takes a lot of effort to support such a monster as wayland compositor. So only big players like Gnome and KDE will stay alive. Others will die.
That seems unlikely. Wayland should be easier to make a window manager/compositor for than X11 because it has a sane design. I expect there to continue to be a robust assortment of Wayland compositors with various behaviors, some ported from X11 window managers, some based on Weston. It would make sense to build from the reference Weston implementation rather than writing your own from scratch.
> Under X11, if somebody wants to write a cool dockbar he can just write it. He don't have to patch Gnome/KDE/X.Org. And he can use it anywhere, in Gnome, KDE or OpenBox
That's not really true, X11 doesn't have any support for dockbars and the like, what there is are standards hammered out over the years by the window manager makers for dockbars and other apps to signal what they expect so that the window manager knows where to put them, not to put borders on them, etc. So they did have to "patch" gnome/kde/xorg to make this work, and continue to make new standards at freedesktop.org for new use cases, you can't take that effort for granted and claim that Wayland would be any different.
> If he wants to write a WM he's free to do it (IIRC, it takes ~50 lines of code for a basic WM)
I call BS, a window manager which supports all the relevant standards you just talked about previously takes far far far more than 50 LoC and has to spend a huge amount of effort to work around unfixable bugs and legacy behaviors because of X11. Nothing is straightforward or easy at this level. All of the logic for how your desktop work is in the window manager.
> Under Wayland one can't just write a dockbar. He must integrate it with some compositor.
That's not any different than X11 for the reasons I mentioned before
> And even if his patches were accepted by e.g. kwin, his dockbar will work under kwin only, but not under weston.
I would expect new versions of the relevant standards that these window managers, such as kwin, already support. It may be even easier than that, much of the expected behavior may just work with very little modification when porting existing desktops to Wayland. I wouldn't expect the major window manager/compositors to radically change their behavior when moving to Wayland, just to spite each other or something.
> X.Org is a pearl of Linux world. It's extremely flexible, whatever you want you can do that.
> X.Org just works.
Not really, the people who maintain that fiction for you have very strongly disagreed, which is why they have created Wayland.
> Are you still saying that there will be X11 support in wayland? And what is it going to be used for?
Yes, of course. X11 will continue to work much the same way it does now into the distant future to support all those 10+ year old applications you may want to run.
> Wayland bring fragmentation to Linux. Under wayland almost everything is compositor-specific. Since it's really hard to make a good compositor, there's going to be just a few of them, and soft written for one compositor, won't work under another one.
Not really true on any point. This will not be any different than today, compatibility is not a function of X11 vs. Wayland but of the window manager/compositor makers like KDE/GNOME/XFCE/Openbox/etc. in having standards. I wouldn't expect anything substantial to change on this front.