Well, it's almost, because only part of it is rewritten.
Wayland is supposed to be just the protocol, whereas
X.Org has a bunch of other things that go with it. Also, if I remember correctly,
Wayland isn't meant to work as a server, so I don't think it offers that powerful functionality as X11 does. So you can use
X.Org along with
Wayland to have that functionality, without any conflicts (at least that's what the authors envisioned), or you can use
Wayland as an
X.Org X Server multiplexer (have several X Sessions opened at the same time). You can use "standalone"
Wayland or
Wayland +
X.Org, or whatever. It's all in that FAQ link. Maybe
this illustration will be helpful too. Even though many of use are probably not excited about
Wayland, we will probably have to get used to it sooner or later.