> There are also wscons issues.  The wscons model assumes a single
> console and multiplexes all input.

Then, for all its benefits, wscons is a rather large step backwards in
that respect, since it certainly used to work fine to configure
multiple keybaords, mice, and screens.  (Getting sessions on other than
the console kbd/mouse/video is not totally trivial, since as far as I
know no ports supported framebuffer terminal emulators other than the
console.  But mechanisms like xdm that don't start from text "consoles"
have always been there.)

> Or even if there is a machine that has the required combination of
> SBus/PCI/UPA/USB/serial hardware to achieve the goal.

Any machine with multiple framebuffers and USB could have multiple
keyboards and mice on it.

Any Sun from the Sun-3 era up through the U2 (and possibly beyond) can
be given a second keyboard and mouse at the cost of the serial ports
with a trivial amount of external hardware by configuring a keyboard
and mouse rather than serial lines on the second serial chip.  Pop a
second framebuffer in there too and you're ready to go hardwarily.

This is partially speculation, but only partially, and that part is
well-grounded.  I have never run two separate X sessions on the same
CPU but separate kbd/ms/vid hardware this way.  I have however run
second X servers on second framebuffers using a virutal second kbd/ms
(I've got a backwards-multiplexer layer that lets me switch a single
physical keyboard/mouse among multiple virtual keyboards/mice).  I have
also put a keyboard on a serial line, including configuring a kbd
instance on the serial chip connected to ttya/ttyb and connecting a
keyboard with appropriate glue electronics (an ICL232 and a 7404, if
memory serves).  I don't recall trying mice, but I see no reason to
think they wouldn't work as well as keyboards.

Put a multi-port serial card in there and an xbox sbus expander chassis
and you could run a half-dozen X sessions off a single CPU.  (In
principle.  The framebuffers should be fine, but you may find that you
can't attach a kbd or ms to the serial device the multiport card shows
up as, at least not without a little config glue.)

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