Up to this step everything worked fine.
But after the reboot i got tiny window decorations. This had to do with some further changes to the unity desktop - i used compiz there and this broke the new wayland configuration.
I found some hints about
dpkg --purge compiz-plugins ...but this did not really help.
The way out was this:
mv .compiz .compiz.oldAfter moving such old configuration directories the desktop looked ok.
mv .gconf .gconf.old
mv .config .config.old
For changing the windows decorations i had to install
apt install gnome-tweak-toolSorry, that i do not post any screenshot of the new 17.10 desktop - but the screenshot application does not work anymore ;-)