> It does work on amd64 for consoles greater than the first one, with
> these changes.

I am completely confused with scrollback.
I have console on the screen 0 (ctrl-alt-f1).
System only dumps logs into it, login is disabled on it:

# in /etc/ttys
console "/usr/libexec/getty Pc"         vt100   off
ttyE0   "/usr/libexec/getty Pc"         vt220   off
ttyE1   "/usr/libexec/getty Pc"         vt220   on secure
ttyE2   "/usr/libexec/getty Pc"         vt220   on secure
ttyE3   "/usr/libexec/getty Pc"         vt220   on secure

# in wscons.conf
# screens to create
#       idx     screen  emul
# Screen 0 is already configured as console in most cases.
#  Uncomment if a serial console is used.
#screen 0       -       vt100
screen  1       -       vt100
screen  2       -       vt100
screen  3       -       vt100
screen  4       -       vt100
screen  5       -       vt100
screen  6       -       vt100
screen  7       -       vt100

But I can scrollback console in screen0 and all ttyE* contrary to your words.
Anyway the only use of scrollback that I can see is to scroolback
bootup messages on console.  When logged in one can use screen(1) with many
more besides scrollback buffer of arbitrary size.

Also I observe weird behaviour of wscons recent monthes.  Sometimes last line
may disappear.  Recent days I repeatedly see contents of one screen appears in another.

--
Denis Lagno,
PGP key fingerprint: F94F F38F 1895 E673 4374 9D63 2B9E FAB3 8E83 584C