It seems to me that this issue is a bug and not a wishlist.
And it's not a bug of kdm either.
The file which is responsible to suppress the userlist in kdm_greeter is
/etc/default/kdm.d/10_desktop-base
which is provided by the package "desktop-base"
This file contains a reference to a theme which does not supply a
userlist.
If you set the variable
USETHEME="false"
then the userlist appears like before.
Don't forget to "/etc/init.d/kdm restart" after this change as there
are some files written to /var/run/kdm/
HTH.
t++
